EXACTECH KNEE - Semantic Scholardesign offers 2 ML/AP ratios per AP size (narrow and standard) for...

E X AC T E C H KNEE

COMPONENT FIT

Clinical Evaluation of Distal Femoral Fit Using Exactech Logic Prosthesis (Internal Publication) ............................ 2

Distal Femoral Morphology and Its Correlation With Two Contemporary TKA Designs (ORS 2017, Abstract 1975) ..... 4

Evaluation of a Western Originated Total Knee Arthroplasty Design on the Fit of Small Sizes Femora (ORS 2016, Abstract 0942) ..................................... 4

ALIGNMENT AND BALANCING

Total Knee Arthroplasty Using a Contemporary Computer-Assisted Surgical System: A Review of Surgical Parameters on More Than 4000 Clinical Cases (CAOS 2016) ............................. 4

Computer-Assisted Total Knee Arthroplasty: Impact of Surgeon Experience on the Ability To Achieve Surgical Resection Goals (CAOS 2016) 5

Computer-Assisted Surgery Provides an Effective And Accurate Tool for Naturally Aligned Total Knee Arthroplasty (ORS 2016, Abstract 1008) ............................ 5

The Effect of Posterior Tibial Slope on the Kinematics of PCL-Retaining Total Knee Arthroscopy (ORS 2016, Abstract 1875) .................................................... 5

Evaluation of Anteroposterior Kinematics During Cruciate-Retaining Total Knee Arthroplasty (ESSKA 2016, Abstract 1188) ...................................... 6

ECONOMIC VALUE

ExactechGPS Guidance System Does Not Increase Operative Time When Compared to Conventionally Instrumented Total Knee Arthroplasty (ORS 2016, Abstract 1979) ................... 6

Technology and Cost-Effectiveness in Knee Arthroplasty: Computer Navigation and Robotics Am J Orthop. 2009;38(2 suppl):32-36. ....................... 6

REVISION

Tibial and Femoral Stem Extension Fatigue Performance With and Without LPB Treatment. (Internal Exactech Publication) .......................................... 7

A Surgeon’s Perspective on Why Navigation is Important in Revision Total Knee Arthroplasty (Exactech Innovations Volume 2, Issue 2, 2016) .. 8

Early Results of a New Revision Total Knee Arthroplasty System Used in the Staged Treatment for Chronic Periprosthetic Infection (Exactech Innovations Volume 2, Issue 2, 2016) .. 8

APPENDIX ........................................ 9

Exactech Scientific and Clinical Evidence

Abstract Summary

2 3

Since we began Exactech more than 30 years ago, our goal has been to help surgeons worldwide make patients

more mobile. Our innovations have been designed with a singular purpose: to improve patient outcomes.

■ COMPONENT FIT

INTRODUCTION

Published Study DesignPatient Ethnicity/

NationalityPatient Gender

Incidence of > 3mm Overhang at

Distal Femur (N Total Subjects)

Loures et al. 2016 [Loures]

Scorpio®Brazilian Male 10% (10)

Brazilian Female 28% (25)

Natural Knee®

Brazilian Male 7.1% (14)

Brazilian Female 40% (20)

NexGen® Standard

Brazilian Male 10% (10)

Brazilian Female 43.5% (23)

Mahoney et al. 2010 [Mahoney] Scorpio®

American Male 26% (176)

American Female 48% (261)

Chung et al. 2015 [Chung]

E.motion Genesis™ II Korean Mixed 5% (1025)

Clarke et al. 2008 [Clark]

NexGen® Legacy® American Male 0% (41)

NexGen® Legacy® Gender

SolutionTM



Dai et al. 2014 [Dai]

Persona™

Caucasian Mixed/Balanced 0% (135)

Indian Mixed/Balanced 0% (74)

Korean Mixed/Balanced 0% (68)

NexGen® Complete Solution

Caucasian Mixed/Balanced 0% (135)

Indian Mixed/Balanced 1.4% (74)

Korean Mixed/Balanced 0% (68)

Sigma®

Caucasian Mixed/Balanced 3.7% (135)


Korean Mixed/Balanced 2.9% (68)

Genesis™ II




Triathlon®




Vanguard®




Table 1: Previously published overhang incidence on other contemporary femoral designs.

CLINICAL EVALUATION OF DISTAL FEMORAL FIT USING

EXACTECH LOGIC PROSTHESIS (INTERNAL PUBLICATION)

Medial or lateral overhang of the femoral component when

placed on the distal femur has been documented to lead to poor

patient outcomes at 5 years [Chau] and may account for 27%

clinically important knee pain [Mahoney]. Studies demonstrate the

differentiating point for clinical significance is 3-4mm [Mahoney,

Chung]. There has been some discussion that appropriate fit may

be compromised in populations other than Caucasian, particularly

in the Asian population. In the following document, 119 TKA knees

were examined for both medial and lateral fit of the femoral

component to the distal femur in Caucasian, Asian, Hispanic

and African American groups, both males and female. Exactech

Logic closely resembles Persona® in femoral bone fit in non-

Caucasian ethnicity groups and in both male/female genders. Table

1 references a literature review of competitive products reports

incidence of >3mm overhang at distal femur (See Table 1).

4 5

DISTAL FEMORAL MORPHOLOGY AND ITS

CORRELATION WITH TWO CONTEMPORARY TKA

DESIGNS (ORS 2017, ABSTRACT 1975)

A computational comparison was completed on 100 knees

(50 Chinese and 50 Caucasian) comparing Exactech Logic

and a recently released competitive design. Exactech Logic

uses varying ML/AP ratios across AP size to closely match

bone morphology and minimize overhang. The competitive

design offers 2 ML/AP ratios per AP size (narrow and

standard) for mid size femurs. Compared to the competitive

design, the distal ML offerings of Exactech Logic design

are narrower in small component sizes, in between the

standard and narrow sizing offerings in median sizes,

and equivalent to the competitive design in large sizes.

Both products demonstrated minimization of component

overhang. Exactech Logic closely resembles a recently

released competitive product in femoral component fit in

non-Caucasian ethnicity groups and in both male/female

genders (See Figure 1).

EVALUATION OF A WESTERN ORIGINATED TOTAL

KNEE ARTHROPLASTY DESIGN ON THE FIT OF SMALL

SIZES FEMORA (ORS 2016, ABSTRACT 0942)

Digital CT segmented surfaces of 80 femurs with <63mm

AP dimension (41 Asian and 39 Caucasian) were used for

this study. Clinically significant overhang was determined

as 3mm or greater in distal component overhang. In

general, the fit of the Logic design was equally good

between both ethnic groups, and out of the 80 knees only

one knee (Asian) showed medial overhang of 3.3mm. In

fact, the results demonstrated less overhang incidences in

the Asian patients compared to previous similar evaluations

on several other western based contemporary designs.

The conclusion was that the Exactech Logic femoral

components can provide equally good fit in small sized

knees for both Asian and Caucasian patients.

■ ALIGNMENT AND BALANCINGTOTAL KNEE ARTHROPLASTY USING A

CONTEMPORARY COMPUTER-ASSISTED SURGICAL

SYSTEM: A REVIEW OF SURGICAL PARAMETERS ON

MORE THAN 4000 CLINICAL CASES (CAOS 2016)

This study looked at 4292 clinical cases to determine

accuracy and precision for the ExactechGPS® system. Two

types of surgical parameters were examined: 1. Planned

resection as defined by the surgeon prior to cuts and 2.

Verification of actual cuts for both the distal femur and

the proximal tibia as determined by the digitalization of

the resected surfaces. All parameters examined were

within 0.5°or 0.2mm of accuracy demonstrating that the

ExactechGPS® system can be used with confidence and

that the surgical resection goals will be achieved with

accuracy and reliability.

COMPUTER-ASSISTED TOTAL KNEE ARTHROPLASTY:

IMPACT OF SURGEON EXPERIENCE ON THE ABILITY

TO ACHIEVE SURGICAL RESECTION GOALS (CAOS

2016)

Novice orthopedic surgeons with <20 CAOS TKA experience

in their practice and no prior computer-assisted experience

compared to highly experienced (>150 TKAs) orthopedic

surgeons showed no statistical differences in planned

verses achieved resections using the ExactechGPS®

system. Accuracy and precision can be achieved at any

level of experience using the ExactechGPS® system.

COMPUTER-ASSISTED SURGERY PROVIDES AN

EFFECTIVE AND ACCURATE TOOL FOR NATURALLY

ALIGNED TOTAL KNEE ARTHROPLASTY (ORS 2016,

ABSTRACT 1008)

This study sought to demonstrate and evaluate a surgical

technique aiming to restore individual natural alignment

in varus knees (>3°). Thirty-four knees were evaluated for

preoperative varus deformity, natural alignment target and

achieved alignment. The ExactechGPS® system provided

the surgeon with the ability to quantify the alignment

targets, guidance to bony resections and assess accuracy

of alignment. The final achieved natural alignment for both

genders were consistent with reported constitutional varus

in healthy population. Natural alignment can be achieved

with accuracy and precision in varus knees using the

ExactechGPS® system.

THE EFFECT OF POSTERIOR TIBIAL SLOPE ON

THE KINEMATICS OF PCL-RETAINING TOTAL KNEE

ARTHROSCOPY (ORS 2016, ABSTRACT 1875)

The purpose of this study was to assess the impact of

posterior tibial slope on the kinematics of an Optetrak

Logic® CR TKA procedure. A specially designed tibial

baseplate allowed the tibial slope to be modified without

additional cuts to avoid potential damage to the soft tissue

envelope. Four slopes were evaluated (10°, 7°, 4°, 1°) in 6

cadaver knees and compared to the native knee state. The

average kinematics for each of the four slopes evaluated

were all close to the native knee. However, the individual

kinematics varied from the average value and exhibited

certain slope preference in order to reproduce native

kinematics (See Figures 2 and 3).

45 50 55 60 65 70

Aspe

ct ra

tio M

L/AP

AP (mm)

Design BDesign A Caucasian Female

Caucasian MaleChinese FemaleChinese Male

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

1.40

1.45

1.50

Figure 1. Aspect ratio of the bone data overlaid with the two contemporary femoral component designs.

The effect of posterior tibial slope on the kinematics of PCL-retaining Total Knee Arthroplasty

Jean-Yves Jenny1, Michael B Cross2, Cyril Hamad3, Fabrice Bertrand3, Laurent Angibaud4, Yifei Dai4

1Hôpitaux Universitaires de Strasbourg, Illkirch, FR, 2Hospital for Special Surgery, New York, NY, USA, 3Blue Ortho, La Tronche, FR, 4Exactech Inc, Gainesville, FL, USA

Disclosures: Jean-Yves Jenny (1-Aesculap Inc, 3B-FH Orthopedics Inc, Exactech Inc), Michael B Cross (1,3B,5-Smith and Nephew PLC, 3B-Exactech Inc, LinkBio Corp, Intellijoint Surgical Inc), Cyril Hamad and Fabrice Bertrand (3A Blue Ortho), Laurent Angibaud, and Yifei Dai (3A,4 Exactech Inc)

Introduction: Total knee arthroplasty (TKA) offers an effective treatment for end-stage knee osteoarthritis. One important goal of the procedure is to restore physiological knee kinematics. However, fluoroscopy studies have shown abnormal postoperative knee kinematics [1] that may lead to suboptimal clinical outcomes [2]. Posterior tibial slope (PTS) of the reconstructed knee may impact postoperative knee kinematics [3] as it directly affects the strain in the posterior cruciate ligament (PCL). However, no consensus has been reached on the most appropriate slope. The goal of the present study was to assess the impact of the PTS on the kinematics of a PCL-retaining TKA. Materials and Methods: Cemented PCL-retaining TKAs (Logic CR, Exactech, Gainesville, FL) were performed on six cadaveric knees (fresh frozen, non-arthritic, PCL presumably intact) using a computer-assisted surgical guidance system (ExactechGPS®, Blue-Ortho, Grenoble, FR). The implanted tibial baseplate was specifically designed with a mechanism to precisely and easily modify the PTS without repeatedly removing/assembling the tibial insert with varying posterior slopes, avoiding potential damages to the soft-tissue envelope (Fig.1). Tibiofemoral internal/external (I/E) rotation, tibiofemoral anteroposterior (AP) translation, and hip-knee-ankle angles (HKA) were evaluated by performing a full passive range of motion (ROM) 3 times on the native knees, and posteroperatively at each of the 4 PTSs (10°, 7°, 4°, and 1°). Knee kinematics were compared between the native state and different PSTs. Results: Average kinematics over the 6 knees showed that all 4 PTSs closely followed the native knee in tibiofemoral I/E rotation, with approximately 15° of tibial internal rotation across the entire flexion range (Fig. 2A). The average HKA of all 4 PTSs were found to follow the similar pattern as in the native knee, which went from neutral HKA at extension to varus at high flexion (~3° for the native knee, ~4-5° for the 4 PTSs) (Fig. 2B). For average tibiofemoral AP translation, all 4 posterior slopes exhibited posterior femoral rollback close to the native knee starting at around 50° leg flexion (Fig. 3B). No clinically significant differences were found between the 4 PTSs. However in contrast to the average data, PTS was found to impact postoperative kinematics with considerable clinical significance (Fig. 3). Discussion: This study applied a soft tissue preserving test method for the measurement of impact of PTS on the postoperative knee kinematics. For the specific TKA design studied, variation of PTS was not found to significantly impact the average post-operative kinematics in the knee. However, the data suggested that patient-specific selection of posterior slope is more favorable in order to achieve more physiological postoperative kinematics. Significance: Average measured postoperative knee kinematics did not suggest a preferred posterior tibial slope for TKA. Proper selection of the posterior slope varies between individual patients. References [1] Banks SA, et al. J Arthroplasty,12, pp: 297-304, 1997; [2] D’Lima DD, et al. Clin Orthop Relat Res, 392, pp: 124-130, 2001; [3] Giffin JR, et al. Am J Sports Med, 32(2), pp: 376-82, 2004; [4] Baier C, et al. Int Orthop, 37(3), pp: 407-14, 2013.

ORS 2016 Annual Meeting Poster No. 1875







■ COMPONENT FIT

* Laboratory testing may not necessarily be predictive of clinical performance.


6 7

1500

2000

2500

3000

0.01 0.1 1 10

Peak

Cyc

lic L

oad

(N)

Cycles Before Failure (Mc)

Exactech: CoCr Tray + Ti stem without LPB

† Exactech: CoCr Tray + Ti stem with LPB

§ Competitive: Ti Tray + Ti stem without LPB

† The 5th sample in the Exactech LPB treated configuation was not tested under the lowest load magnitude as a sample evaluted at a higher load had successfully completed 10 Mc.

§ Tests on competitive configuration at higher load magitudes were unnecessary as itfailed early under the lowest test load. A total of two samples were tested at the lowest loadto confirm the observation of early failure.

Figure 2: Force versus cycle before failure are plotted for the treated and untreated CoCr tibial tray and titanium stem extension assemblies, and competitive samples.

EVALUATION OF ANTEROPOSTERIOR KINEMATICS

DURING CRUCIATE-RETAINING TOTAL KNEE

ARTHROPLASTY (ESSKA 2016, ABSTRACT 1188)

In a CR Total Knee Arthroplasty, anterior sliding of the

distal femur relative to the proximal tibia during mid-

flexion extension can result in abnormal AP kinematics,

limitations in ROM and increase in polyethylene wear.

ROM test was performed on Exactech Logic CR knees at

four posterior tibial slopes (10°, 7°, 4°, 1°) for tibiofemoral

displacement in AP direction. The kinematics exhibited

no paradoxical motion throughout the flexion range. The

results demonstrate stable and natural AP kinematics using

the Optetrak Logic® CR design.

TIBIAL AND FEMORAL STEM EXTENSION

FATIGUE PERFORMANCE WITH AND WITHOUT LPB

TREATMENT. (INTERNAL EXACTECH PUBLICATION)

Low Plasticity Burnishing (LPB) is a novel treatment

process for titanium material to improve surface finish,

increase corrosion resistance, and enhance fatigue

performance. This process is applied to Logic CC tibial and

femoral stem extensions. Fatigue testing was performed

on Exactech stem extensions treated with and without LPB

process and a comparable DePuy Synthes stem extension.

Both Exactech stem extensions, with and without the LPB

treatment, had better fatigue performance than the DePuy

Synthes design. The DePuy Synthes stem extension failed

first, followed by Exactech non LPB treated stem, and finally

the Exactech LPB treated stem. The LPB treated Exactech

stem had >60,000% increase in fatigue performance

compared to the DePuy Synthes design. The LPB treated

stem extension may offer a better solution for younger,

more active patient populations (Figure 2).

EXACTECHGPS® GUIDANCE SYSTEM DOES NOT

INCREASE OPERATIVE TIME WHEN COMPARED TO

CONVENTIONALLY INSTRUMENTED TOTAL KNEE

ARTHROPLASTY

This study compares total surgical time for primary TKA

using both conventional technique and ExactechGPS®.

It also reviewed surgical time variations between an

experienced CAOS surgeon and an early experienced CAOS

surgeon. Initially, the early experience group increased the

surgical time by an average of 7 minutes. However, with

an advanced CAOS experience level, the surgeon was able

to achieve time neutral (statistically insignificant) with an

average of 2 minutes saving compared to conventional

technique. The results demonstrated that ExactechGPS®

does not necessarily increase surgical time compared to

conventional technique.

TECHNOLOGY AND COST-EFFECTIVENESS IN KNEE

ARTHROPLASTY: COMPUTER NAVIGATION AND

ROBOTICS AM J ORTHOP. 2009;38(2 SUPPL):32-36.

Only 3-5% of knee replacement surgeries use navigation

technology, despite the evidence of improved radiographic

alignment- the main reason is cost. A retrospective review

on cases between 2004 and 2007 was performed in a

200 bed hospital with an annual volume of 1000+ joints.

One surgeon’s data using computer-assisted surgery

was compared to the combined hospital surgical data

and national average, using conventional methods for

joint replacement. The single surgeon data demonstrated

length of stay (LOS) as less than 3 days for all hip and

knee arthroplasty using CAS as compared with the

average 3-4 day Medicare, national and hospital combined

data. The surgeon’s discharge to home rate was 71%;

triple that of Medicare, national and combined hospital

data for 2005-2006. The cost for navigated TKAs was

actually $4-5K less per case than national and hospital

averages with conventional TKA. Clinical volume growth

is expected with this type of novel technology and

was documented in this hospital at 310% growth in

the first year as a result of public relations initiatives

and primarily as a result of word of mouth. For new

orthopedic technology to be widely adopted there must

have favorable net revenue for institutions, less strain

on systems, improved patient outcomes with implant

durability and increased demand from consumers. CAS

was demonstrated to be cost-effective in this cohort

without increasing the burden on the hospital work flow.

Average charges for navigation, LOS, and incidence of

discharge to home may actually be lower than CMS,

national or combined hospital reported data.

■ ECONOMIC VALUE

■ REVISION■ ALIGNMENT AND BALANCING


8 9

■ APPENDIX

A SURGEON’S PERSPECTIVE ON WHY NAVIGATION

IS IMPORTANT IN REVISION TOTAL KNEE

ARTHROPLASTY (EXACTECH INNOVATIONS VOLUME

2, ISSUE 2, 2016)

Most orthopedic surgeons currently using a CAOS system

aim to achieve better alignment, reduce surgical time,

reduce number of instruments, avoid violating the IM canal

and manage pre-post kinematics. The Exactech RTKA GPS

system is designed for ease of use, regardless of the level

of experience with any CAOS system. Dr. Huddleston who

has over 750 revisions performed shares his experience

using the ExactechGPS system for revision- he provides

insights on why he believes the revision platform will

be easier to use, more efficient and result in improved

functional outcomes.

EARLY RESULTS OF A NEW REVISION TOTAL KNEE

ARTHROPLASTY SYSTEM USED IN THE STAGED

TREATMENT FOR CHRONIC PERIPROSTHETIC

INFECTION (EXACTECH INNOVATIONS VOLUME 2,

ISSUE 2, 2016)

This paper reviewed 7 revision TKA cases for treatment

of chronic periprosthetic infection performed by a single

surgeon using the Optetrak Logic® CC revision system. In

all the cases, the Logic CC system was shown to offer an

effective solution with regard to implant removal (especially

with well fixed implants in the setting of weakened bone),

bone preparation (in the setting of weakened fixation

platform), articular constraint, fixation dependability, and

bone defect management. The advantages of two unique

instruments were highlighted for implant removal; the

Exactech AcuDriver® (a specialized pneumatic cement-

implant disruption system) and the Exactech Extractor

(axial force device used to remove the implant verses a

compressive, bending or torsional forces to help reduce

potential fractures or additional bone loss). The stem offset

offerings achieved optimal femoral stability, with bony used

defects and voids properly managed by a variety of cones

and augment solutions. A wide selection of constraint

options were used to address varying levels of collateral

ligament competence. The surgeon believes that the

Logic CC Revision system offers features and options that

allow for the management of virtually any revision knee

arthroplasty scenario.

■ REVISION ■ APPENDIX

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■ APPENDIX

10

■ APPENDIX

Clinical Evaluation of Distal Femoral Fit Using Exactech Logic® Prosthesis

Yifei Dai Ph.D., Weimin Yue Ph.D., Herbert M Bertram M.D., Richard J Friedman M.D., Chul-‐Won Ha M.D. Ph.D., James I Huddleston M.D., Raymond P Robinson M.D., Laurent D Angibaud M.S.

Introduction

Over more than 40 years of the history of total knee arthroplasty (TKA), the treatment evolved from targeting pain relief and restoration to basic functions in the general patient population, to a surgery with comprehensive consideration of individual’s characteristics with regard to both prosthesis design and surgical techniques. Such considerations include adequate component fit, accurate balancing of the joint gaps, proper post-‐operative kinematics, minimized infection rates, and so on and so forth. Among these considerations, the call for adequate component fit is linked to the underlying clinical concern on the overhanging of the components. Component overhang has been shown to lead to poor patient outcomes at 5 years post-‐operatively [Chau], and may account for 27% of clinically relevant knee pain after TKA [Mahoney], possibly due to irritation of the knee tendons and ligaments [Dennis]. Especially in the femur, the goal of minimizing component overhang can be complicated by the other surgical targets. For example, as overhang can be avoided by undersizing the femoral component, the undersized component anteroposterior (AP) dimension can increase flexion laxity and/or result in anterior notching. Although these situations may be resolved by additional femoral resections to prepare for the undersized femur, the joint line will be inevitably elevated that can negatively impact patellofemoral kinematics, increase the incidence of instability, introduce excessive polyethylene wear, decrease knee flexion range, and cause anterior knee pain [Belleman, Yoshii, Figgie, Laskin, Singerman].

Studies have identified that an overhang of 3-‐4mm is the differentiating point for clinical importance [Mahoney, Chung]. In a 2010 study, Mahoney et al. reported that more than 3 mm of component overhang can increase the risk of clinically important knee pain by 90% [Mahoney]. Also, a recent investigation by Chung et al concluded that more than 4mm of overhang can significantly lower the maximum flexion angle postoperatively [Chung]. These findings confirmed that proper component fit to the distal femur is critical for the success of the TKA, which emphasize the need for the continuous evaluation on the morphological fit of the current femoral component designs.

Several morphological analyses have reported varying degrees of femoral fit in several globally marketed contemporary TKA systems, ranging from none to moderate-‐severe overhang incidences (Table 1). Also, these studies demonstrated that within the same design, the goodness of fit can vary between both genders and different ethnicities. To compare the fit of the Exactech Optetrak Logic® design with the published data on other contemporary designs, a clinical assessment of the Logic femoral design was carried out by a collaboration between Exactech and several clinical sites. The objective of this study was to clinically assess the fit of the Logic femoral components against the anatomy from a group of multiethnic TKA patients.

Published Study Design

Patient Ethnicity/Nationality Patient Gender

Incidence of > 3mm Overhang at Distal Femur

(N Total Subjects)

Loures et al. 2016 [Loures]

Scorpio® Brazilian Male 10% (10) Brazilian Female 28% (25)

Natural Knee®

Brazilian Male 7.1% (14) Brazilian Female 40% (20)

NexGen® Standard

Brazilian Male 10% (10) Brazilian Female 43.5% (23)

Mahoney et al. 2010 [Mahoney] Scorpio®

American Male 26% (176) American Female 48% (261)

Chung et al. 2015 [Chung]

E.motion Genesis™ II

Korean Mixed 5% (1025)

Clarke et al. 2008 [Clark]

NexGen® Legacy®

American Male 0% (41)

NexGen® Legacy® Gender

SolutionTM



Dai et al 2014 [Dai]

Persona™ Caucasian Mixed/Balanced 0% (135)

Indian Mixed/Balanced 0% (74) Korean Mixed/Balanced 0% (68)

NexGen® Complete Solution

Caucasian Mixed/Balanced 0% (135) Indian Mixed/Balanced 1.4% (74) Korean Mixed/Balanced 0% (68)

Sigma® Caucasian Mixed/Balanced 3.7% (135)

Indian Mixed/Balanced 2.7% (74) Korean Mixed/Balanced 2.9% (68)

Genesis™ II Caucasian Mixed/Balanced 20.7% (135)


Triathlon® Caucasian Mixed/Balanced 7.4% (135)


Vanguard® Caucasian Mixed/Balanced 20.0% (135)


Table 1: Previously published overhang incidence on other contemporary femoral designs.

Materials and methods

TKA Surgeries

A total of 119 knees subjected to primary TKA were included in this study. The patients were recruited from multiple ethnicities, with both genders included (Table 1). Exclusion criteria were: 1) previous

13

■ APPENDIX

12

■ APPENDIX

trauma in the knee and 2) existence of severe preoperative knee deformities (defined as preoperative varus/valgus alignment > 10°, flexion contracture > 15°, and range of motion < 90°).

Ethnicity Total (N) Female (N) Male (N)

Caucasian 64 40 24

Asian 30 23 7

Hispanic 10 4 6

African American 15 12 3

Table 2. Ethnic and gender distribution of the study subjects.

Five senior surgeons, each from an individual surgical center, performed primary TKA surgeries using Exactech Optetrak Logic® knee prostheses on the recruited knees. The surgeries were carried out followed each individual surgeon’s standard practice, with the common target of neutral varus/valgus alignment, 0° flexion/extension, and 10 mm resection depth according to the surgical techniques of the Logic implant system [surg tech].

Distal femoral fit assessment

After sizing and implanting the femoral component, the surgeon used a gauge specifically designed by Exactech for this study to measure the medial and lateral fit (over-‐ or under-‐ hang) at the anteroposterior (AP) middle point of the distal resection surface (Fig 1). The difference between bony edge of the resection and the femoral component was assessed for pooled data and each gender/ethnicity. The percentage of acceptable component fit (≤ 3 mm overhang) and the incidence of clinically important overhang (> 3 mm) were assessed across the bones, and per gender/ethnicity. Statistical significance was defined as p < 0.05.

Figure 1. Illustration of distal femoral component fit measurement using the special gauge.

Results

A summary of over-‐/under-‐ hang incidences is presented in Table 2. Across genders and ethnicities, the Logic femoral component consistently minimized clinically important overhang. Only 1 knee (Asian, female, medium femoral size 3.0) out of the 119 studied had clinical important overhang slightly over 3 mm (4 mm).

Discussion

Released in 2009, Exactech Optetrak Logic design continues the successful evolution of the Exactech Optetrak knee system. Optetrak Logic allows today’s patients a greater range of motion and patella function necessary to maintain their activity and independence. The system has demonstrated excellent clinical long-‐term clinical results around the world [Robinson, Edwards, Ehrhardt].

One of the key reasons for the clinical success of the Logic design, as confirmed by the findings in this study, may be dedicated to the sizing of the femoral components. This multi-‐center implantation study on the fit of the Logic femoral components demonstrated extremely low incidence of clinically important femoral component overhang (near 0% incidence), suggesting minimal risk of soft-‐tissue impingement related complications with the use of this design. In addition, contrary to the common belief that the fit of western originated knee designs may be compromised in other populations, especially Asian [Yue, Chung, Loures], the Logic femoral design was shown to provide equally good fit for all 4 ethnic groups studied. In addition, although it has been reported that component fit in the female knees is inferior to that in the male knees [Loures, Mahoney], the Logic design did not demonstrate gender-‐dependence in this study. A summary of published overhang incidences using various knee designs is presented in Table 3. Compared to the published studies, the low incidence of clinically important overhang in Logic was demonstrated to be comparable to the designs with the availability of gender solutions (Table 3).

Clinical assessment on the distal femoral fit of the Exactech Optetrak Logic® femoral component design demonstrated minimal (near zero) incidence of clinically important overhang in both genders and 4 ethnic groups. The data confirmed that the sizing of the Logic femoral component respects the anatomy of the distal femur, potentially minimizing the risk of TKA complications related to femoral component overhang.

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■ APPENDIX

Medial Lateral

Female Male Female Male

Mean (mm) -‐3.4 -‐5.4 -‐2.2 -‐1.4

Standard Deviation (mm) 2.4 2.4 2.2 1.9

Max Overhang (mm) 2.0 0.0 2.0 4.0

% Clinically Important Overhang

0.0% 0.0% 0.0% 1.3%

B

Medial Lateral

Caucasian Asian Hispanic African American Caucasian Asian Hispanic

African American

Mean (mm) -‐4.9 -‐2.2 -‐5.0 -‐3.7 -‐2.0 -‐0.1 -‐4.8 -‐1.6 Standard

Deviation (mm) 2.2 2.1 2.8 2.9 1.6 1.7 2.3 1.6

Max Overhang (mm) 2.0 1.0 0.0 0.0 2.0 4.0 -‐2.0 0.0

% Clinically Important Overhang

0.0% 0.0% 0.0% 0.0% 0.0% 3.3% 0.0% 0.0%

Table 3. A) Medial and lateral fit of the femoral component for each gender. B) Medial and lateral fit of the femoral component for each ethnicity. Positive millimeter values indicate component overhang, negative millimeter values indicate component underhang.

References

[1] Chau R, Gulati A, Pandit H, Beard DJ, Price AJ, Dodd CAF, Gill HS, Murray DW (2009) Tibial component overhang following unicompartmental knee replacement: does it matter? Knee 16:310–313

[2] Mahoney OM, Kinsey T (2010) Overhang of the femoral component in total knee arthroplasty: risk factors and clinical consequences. J Bone Joint Surg Am 92(5):1115–1121

[3] Dennis DA (2004) Evaluation of painful total knee arthroplasty. J Arthroplasty 19(4 Suppl 1):35–41 [4] Bellemans J (2004) Restoring the joint line in revision TKA: does it matter? Knee 11:3–5 [5] Yoshii I, Whiteside LA, White SE, Milliano MT (1991) Influence of prosthetic joint line position on

knee kinematics and patellar position. J Arthroplasty 6:169–177 [6] Figgie HE, Goldberg VM, Heiple KG, Moller HS, Gordon NH (1986) The influence of tibial-‐

patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg Am 68:1035–1040

[7] Laskin RS (1998) Management of the patella during revision total knee replacement arthroplasty. Orthop Clin North Am 29:355–360

[8] Singerman R, Davy DT, Goldberg VM (1994) Effects of patella alta and patella infera on patellofemoral contact forces. J Biomech 27:1059–1065

[9] Chung BJ, Kang JY, Kang YG, Kim SJ, Kim TK (2015) Clinical Implications of Femoral Anthropometrical Features for Total Knee Arthroplasty in Koreans. J Arthroplasty 30(7):1220-‐1227

[11] Loures FB, de Araújo Góes RF, da Palma IM, Labronici PJ, Granjeiro JM, Olej B (2016) Anthropometric study of the knee and its correlation with the size of three implants available for arthroplasty. Rev Bras Ortop 51(3):282-‐289

[12] Clarke HD, Hentz JG (2008) Restoration of femoral anatomy in TKA with unisex and gender specific components. Clin Orthop Relat Res 466:2711

[13] Dai Y, Scuderi GR, Penninger C, Bischoff JE, Rosenberg A (2014) Increased shape and size offerings of femoral components improve fit during total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 22(12):2931-‐2940

[14] Optetrak Logic® CR/PS low profile instrumentation (LPI®) operative technique. Rev. C 0515 [15] Robinson RP, Green TM (2011) Eleven-‐year implant survival rates of the all-‐polyethylene and metal

backed modular Optetrak posterior stabilized knee in bilateral simultaneous cases. J Arthroplasty 26(8):1165-‐1169

[16] Edwards J, Gradisar I Jr, Nadaud M, Kovacik M, Askey M (2004) Eight and one-‐half year clinical experience with the Optetrak total knee prosthesis. Presented at the American Academy of Orthopedic Surgeons

[17] Ehrhardt J, Gadinsky N, Lyman S, Markowicz D, Westrich G (2011) Average 7-‐year survivorship and clinical results of a newer primary posterior stabilized total knee arthroplasty HSS J 7(2):120-‐124

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Distal femoral morphology and its correlation with two contemporary TKA designsYifei Dai1, Wemin Yue1, Julien Deckx2, Mike Lawrenchuk2, Laurent Angibaud1,

1Exactech Inc, Gainesville, FL, USA; 2Materialise NV, Leuven, Belgium

Disclosures: Yifei Dai, Weimin Yue, and Laurent Angibaud (3A,4 Exactech Inc), Julien Deckx and Mike Lawrenchuk (3A Materialise NV)

INTRODUCTION: Morphological fit of the femoral component is important for the success of total knee arthroplasty (TKA) [1], as mismatched femoral component size may affect proper flexion-extension gap balancing, patellofemoral kinematics, and tension in soft tissue. Furthermore, it has been shown that excessive femoral overhang (more than 3mm) is related to postoperative knee pain [2], and this phenomenon is believed to be more prevalent in Asian knees compared to Caucasian knees. To avoid the negative impact from excessive overhang, it is important to understand ethnic differences in the distal femoral morphology, and its correlation to contemporary, especially the most recently released TKA designs. The purpose of this study was to evaluate distal femoral morphology in Asian and Caucasian knees and compare to two new TKA designs.

METHODS: Digital femoral surface models of 50 Chinese (25M/25F) and 50 Caucasian (25M/25F) were used in this study. The anteroposterior (AP) dimension of the femur was measured from the anterior cortex point to the tangent plane of both posterior condyles. A distal TKA resection was then performed virtually on each femur (3 Matic Research v9, Materialise NV, Leuven, Belgium). The mediolateral dimension (ML) of the bones was measured at the anteroposterior mid-point of the distal resection. AP and ML dimensions, as well as the aspect ratio (ML/AP), were compared between the two ethnicities. The bone data was then compared to two contemporary femoral implant designs with different sizing philosophies. Design A has multiple ML size offerings in the mid-size range. Design B has single ML offerings across AP size. Statistical significance was defined as p<0.05.

RESULTS: Significant differences found between ethnicities and genders were presented in Table 1. The majority of the differences were between male and female, but not so much for ethnicity. Both the two contemporary designs assessed had component aspect ratios following the lower bound of the bone data across the sizes, therefore minimizing overhang (Fig. 1). Design B was shown to have aspect ratios slightly lower than Design A in small sizes, in between the two sizing offerings of Design A in median sizes, and matching Design A in large sizes.

DISCUSSION: The study compared femoral morphology between the Chinese knees and Caucasian knees, and demonstrated the majority of the differences exist between genders for these two ethnicities studied. The two newly released contemporary designs both have aspect ratios at the lower bound of the bone data, which can be translated to minimized component overhang in the dataset. Compared to the design philosophy to have multiple ML offerings, Design B varies the aspect ratio across the bone size range to match the morphology of the distal femoral resection.

SIGNIFICANCE: Virtual analysis of 100 femora demonstrated gender and ethnic differences in distal resection morphology between Caucasian and Chinese. Two newly released contemporary femoral component designs with different sizing philosophies (single and multiple ML offerings) bothdemonstrate minimization of component overhang.

REFERENCES: [1] Bonnin MP, et al, Knee Surg Sports Traumatol Arthrosc 2013; [2] Mahoney OM, et al, J Bone Joint Surg Am 2010.

Evaluation of a Western Originated Total Knee Arthroplasty Design on the Fit of Small Sized FemoraWeimin Yue1, Morganne Theobald1, Julien Deckx2, Mike Lawrenchuk2, Laurent Angibaud1

1Exactech Inc, Gainesville, FL, USA 2Materialise NV, Leuven, Belgium

Disclosures: W. Yue: 3A; Exactech Inc. M. Theobald: 3A; Exactech,Inc. M. Lawrenchuk: 3A; Materialise NV. J. Deckx: 3A; Mateialise NV.L. Angibaud: 3A; Exactech,Inc.

INTRODUCTION: Morphological fit of the femoral component is important for the success of total knee arthroplasty (TKA) [1]. Less than 3mm component overhang has been reported to be acceptable to avoid postoperative knee pain [2]. For TKA designs originated from western populations, it is commonly believed that they may not provide optimal fit in small sized femora, especially in Asian knees [3]. This phenomenon may be attributed to difference of anteroposterior (AP) / mediolateral (ML) aspect ratios between the smaller and larger sized femurs. The purpose of this study was to evaluatedistal femoral component fit (ML) of a western originated implant family in the small sized femora (both Chinese and Caucasian).

METHODS: Digital CT segmented surfaces of 80 healthy femora with less than 63mm AP dimension were used for this study (41 Chinese, 39 Caucasian).The selection criterion for the AP dimension was pre-determined based on the lower sizing spectrum of the TKA design system intended to investigate (component AP dimension ranges from 47-74mm). The femora were sized and resected following design-specific sizing and surgical techniques (3 Matic Research v9, Materialise NV, Leuven, Belgium). The corresponding sized femoral component from the design was then placed on each resected distal femur. The ML dimensional mismatch (overhang/underhang) between the bony resection and the placed component was measured at 50% AP location of the distal resection (Figure 1). Any overhang that was greater than 3mm was identified as clinically significant [2]. The fit between Caucasian and Chinese femora was compared, with statistical significance defined as p<0.05.

RESULTS: The dimensional mismatch between the femoral components and the distal resection were listed in Table 1, with overhang noted as “+” and underhang noted as “-”. Only 1 bone having more than 3mm overhang (3.3 mm, medial side, Chinese, Size No. 2) was observed across all 6 smallest sizes of the considered TKA system. No statistical differences were found between the component fit in Chinese and Caucasian femora for either medial (p=0.13) or lateral (p=0.69) side (Table 2).

DISCUSSION: The design investigated in this study, although originated from western populations, provided proper morphological fit to the Chinese distal femur without significant overhang when properly sized. The results demonstrated less overhang incidences in the Asian patients compared to previous similar evaluations on other western based contemporary designs [4]. The femoral components fit both Chinese and Caucasian femora equally well with no significant overhang. This may be attributed to the proper and graduate changes of the component shape (i.e. aspect ratio) for the small sized femora. Future evaluation may include expanding the study to other Asian ethnicities as well as other location(s) of the distal femur.

SIGNIFICANCE: Depending on design, western originated femoral implants can provide good fit in small sized femora. The fit was shown to be equally well between Chinese and Caucasian femora.

REFERENCES:[1] Bonnin MP, et al, Knee Surg Sports Traumatol Arthrosc. 2013 (21):2314-24[2] Mahoney OM, et al, J Bone Joint Surg Am. 2010(92)1115-21[3] HA CW, et al.,J Bone Joint Surg Br. 2012(94-B):638-41[4] Dai Y, et al, Knee Surg Sports Traumatol Arthrosc. 2014 (22):2931-40

IMAGES AND TABLES:Table 1.Dimensional mismatch results between femoral components and distal resection

Implant Size

ComponentAP (mm)

ComponentML (mm)

Number of femora

Number of femora with >3mm overhang (% total femora)

Medial mismatch (mm, mean±std)

Lateral mismatch (mm, mean±std)

No. 1 50.5 55.1 3 0 -4.0 ± 2.4 -4.6 ± 0.4No. 2 53.4 57.4 8 0 -4.1 ± 1.1 -4.2 ± 1.7No. 3 56.6 59.9 21 1 (4.8%) -3.1 ± 2.3 -3.2 ± 1.5No. 4 58.6 62.5 11 0 -2.0 ± 2.4 -2.2 ± 1.9No. 5 60.7 65.0 17 0 -2.6 ± 2.5 -4.4 ± 2.0No. 6 62.7 67.6 20 0 -2.1 ± 2.5 -2.4 ± 2.3

Table 2. Femoral component fit results for Chinese and Caucasian femoraMismatch side

Chinese(mm, mean±std)

Caucasian(mm, mean±std)

Significance

Medial -2.3 ± 2.4 -3.1 ± 2.3 p=0.13Lateral -3.2 ± 2.2 -3.4 ± 1.9 p=0.69

Figure 1. Measurement for femoral component (translucent green color) overhang/underhang over resected femoral surface (purple color).


Evaluation of a Western Originated Total Knee Arthroplasty Design on the Fit of Small Sized FemoraWeimin Yue1, Morganne Theobald1, Julien Deckx2, Mike Lawrenchuk2, Laurent Angibaud1

1Exactech Inc, Gainesville, FL, USA 2Materialise NV, Leuven, Belgium

Disclosures: W. Yue: 3A; Exactech Inc. M. Theobald: 3A; Exactech,Inc. M. Lawrenchuk: 3A; Materialise NV. J. Deckx: 3A; Mateialise NV.L. Angibaud: 3A; Exactech,Inc.

INTRODUCTION: Morphological fit of the femoral component is important for the success of total knee arthroplasty (TKA) [1]. Less than 3mm component overhang has been reported to be acceptable to avoid postoperative knee pain [2]. For TKA designs originated from western populations, it is commonly believed that they may not provide optimal fit in small sized femora, especially in Asian knees [3]. This phenomenon may be attributed to difference of anteroposterior (AP) / mediolateral (ML) aspect ratios between the smaller and larger sized femurs. The purpose of this study was to evaluatedistal femoral component fit (ML) of a western originated implant family in the small sized femora (both Chinese and Caucasian).

METHODS: Digital CT segmented surfaces of 80 healthy femora with less than 63mm AP dimension were used for this study (41 Chinese, 39 Caucasian).The selection criterion for the AP dimension was pre-determined based on the lower sizing spectrum of the TKA design system intended to investigate (component AP dimension ranges from 47-74mm). The femora were sized and resected following design-specific sizing and surgical techniques (3 Matic Research v9, Materialise NV, Leuven, Belgium). The corresponding sized femoral component from the design was then placed on each resected distal femur. The ML dimensional mismatch (overhang/underhang) between the bony resection and the placed component was measured at 50% AP location of the distal resection (Figure 1). Any overhang that was greater than 3mm was identified as clinically significant [2]. The fit between Caucasian and Chinese femora was compared, with statistical significance defined as p<0.05.

RESULTS: The dimensional mismatch between the femoral components and the distal resection were listed in Table 1, with overhang noted as “+” and underhang noted as “-”. Only 1 bone having more than 3mm overhang (3.3 mm, medial side, Chinese, Size No. 2) was observed across all 6 smallest sizes of the considered TKA system. No statistical differences were found between the component fit in Chinese and Caucasian femora for either medial (p=0.13) or lateral (p=0.69) side (Table 2).

DISCUSSION: The design investigated in this study, although originated from western populations, provided proper morphological fit to the Chinese distal femur without significant overhang when properly sized. The results demonstrated less overhang incidences in the Asian patients compared to previous similar evaluations on other western based contemporary designs [4]. The femoral components fit both Chinese and Caucasian femora equally well with no significant overhang. This may be attributed to the proper and graduate changes of the component shape (i.e. aspect ratio) for the small sized femora. Future evaluation may include expanding the study to other Asian ethnicities as well as other location(s) of the distal femur.

SIGNIFICANCE: Depending on design, western originated femoral implants can provide good fit in small sized femora. The fit was shown to be equally well between Chinese and Caucasian femora.

REFERENCES:[1] Bonnin MP, et al, Knee Surg Sports Traumatol Arthrosc. 2013 (21):2314-24[2] Mahoney OM, et al, J Bone Joint Surg Am. 2010(92)1115-21[3] HA CW, et al.,J Bone Joint Surg Br. 2012(94-B):638-41[4] Dai Y, et al, Knee Surg Sports Traumatol Arthrosc. 2014 (22):2931-40

IMAGES AND TABLES:Table 1.Dimensional mismatch results between femoral components and distal resection

Implant Size

ComponentAP (mm)

ComponentML (mm)

Number of femora

Number of femora with >3mm overhang (% total femora)

Medial mismatch (mm, mean±std)

Lateral mismatch (mm, mean±std)

No. 1 50.5 55.1 3 0 -4.0 ± 2.4 -4.6 ± 0.4No. 2 53.4 57.4 8 0 -4.1 ± 1.1 -4.2 ± 1.7No. 3 56.6 59.9 21 1 (4.8%) -3.1 ± 2.3 -3.2 ± 1.5No. 4 58.6 62.5 11 0 -2.0 ± 2.4 -2.2 ± 1.9No. 5 60.7 65.0 17 0 -2.6 ± 2.5 -4.4 ± 2.0No. 6 62.7 67.6 20 0 -2.1 ± 2.5 -2.4 ± 2.3

Table 2. Femoral component fit results for Chinese and Caucasian femoraMismatch side

Chinese(mm, mean±std)

Caucasian(mm, mean±std)

Significance

Medial -2.3 ± 2.4 -3.1 ± 2.3 p=0.13Lateral -3.2 ± 2.2 -3.4 ± 1.9 p=0.69

Figure 1. Measurement for femoral component (translucent green color) overhang/underhang over resected femoral surface (purple color).


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TOTAL KNEE ARTHROPLASTY USING A CONTEMPORARY COMPUTER-ASSISTED SURGICAL SYSTEM: A REVIEW OF SURGICAL PARAMETERS ON MORE THAN 4000 CLINICAL CASESFabrice Bertrand BS1, Yifei Dai PhD2*, Laurent Angibaud BS2, Cyril Hamad BS1, Amaury Jung BS1, David Liu MBBS FRACS3

1 Blue Ortho, La Tronche, 38700, FR2*Exactech Inc, Gainesville, FL, 32653, USA, [email protected] The Gold Coast Centre for Bone and Joint Surgery, Queensland, 4224, AU

INTRODUCTIONComputer-assisted orthopaedic surgery (CAOS) has been shown to offer increased accuracy to the bony resections compared to the conventional techniques [1] but may be dependent on the actual system used and how the algorithm for bone resections are calculated. Previous studies of CAOS have mostly focused on alignment outcomes, based on a small number of patients from selected hospital sites [1]. Several meta-analyses on the outcomes of CAOS have been reported [2,3]. However, these analyses did not differentiate between CAOS systems, while system-dependency has been reported to influence alignment parameters [4].To date, limited information is available to benchmark the ability of a specific CAOS system for its efficiency in achieving the intraoperative surgical goals based a large number of clinical cases. The purpose of this study is to assess the accuracy and precision of achieving surgical goals in more than 4000 cases using a specific contemporary CAOS system.

MATERIALS AND METHODSSurgical parameters (alignment and depth of resections) were extracted from the technical logs of 4292 TKA surgeries performed between October 2012 and January 2016 using acontemporary CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR). The logs did not contain any information related to patient demographics or identity. The following surgical parameters were investigated: 1) planned resection, defined by the surgeon prior to the bone cuts. These parameters serve as inputs for the CAOS guidance; 2) Checked resection, defined as digitalization of the actual resection surfaces by manually pressing an instrumented checker onto the bony cuts. The resection of the distal femur and tibial were evaluated for the study.Deviations in alignment and resection depths (on the referenced side) between planned andchecked resections were calculated in coronal and sagittal planes for both tibia and femur(planned vs checked). Furthermore, a subset of the cases contained a navigated step for gap balancing. The mediolateral (medial/lateral ratio) and flexion-extension (flexion/extensionratio) asymmetry of the joint gap was assessed based on the available data, with a ratio of 1 indicating a perfectly symmetric gap.

RESULTSFor the tibial resection, deviations in coronal alignment (tibial varus/valgus angle), sagittal alignment (posterior tibial slope), and resection depth were -0.05 ± 0.88°, 0.02 ± 1.58°, and 0.14 ± 1.54 mm, respectively (Fig. 1). For the femoral resection, the deviation in coronal alignment (femoral varus/valgus angle), sagittal alignment (femoral flexion), and resectiondepth were 0.00 ± 0.93°, 0.32 ± 1.39°, and 0.05 ± 1.33 mm, respectively (Fig. 1).

Mediolateral gap asymmetry was 0.99 ± 0.16 and 1.01 ± 0.19 for extension and flexion,respectively. Flexion-extension gap asymmetry was 1.15 ± 0.38 and 1.11 ± 0.44 for medial compartment and lateral compartment, respectively (Fig. 2).

DISCUSSIONAn instrument platform for TKA should provide assistance in bony resections that match the target with accuracy and reproducibility, as well as the ability to help properly define joint gaps when needed. This study demonstrated that the specific CAOS system used can offer accurate and precise intra-operative guidance to the surgeon in achieving his/her surgical resection goals. Numerous studies have shown that malalignment can lead to complications, such as component loosening, instability, polyethylene wear, and patellar instability [8-10]. TKA performed using conventional instruments is reported to achieve satisfactory lower limb alignment (within ±3° of varus/valgus relative to the mechanical axis) in only 70-80% of cases [3,5], which may be one of the factors contributing to 20% of patients being dissatisfied with the results of surgery [7]. This study reviewed a large number of cases spanning the application history of the specific CAOS system, providing a complete clinically relevant evaluation of its accuracy and precision in terms of bony resection. We believe surgeons can use this specific CAOS system with confidence that the surgical resection goals will be reproduced with accuracy and reliability.

REFERENCES[1] Sparmann M, et al. Positioning of total knee arthroplasty with and without navigation support: a prospective, randomised study, J Bone Joint Surg Br, 85(6):830-5, 2003.

[2]Brin YS, et al. Imageless computer assisted versus conventional total knee replacement. A Bayesian meta-analysis of 23 comparative studies, Int Orthop, 35(3):331-9, 2011.

[3] Hetaimish BM, et al. Meta-analysis of navigation vs conventional total knee arthroplasty. J Arthroplasty, 27(6):1177-82, 2012.

[4] Carli A, et al. Inconsistencies between navigation data and radiographs in total knee arthroplasty are system-dependent and affect coronal alignment, Can J Surg, 57(5):305-13,2014.

[5] Ensini A, et al. Alignments and clinical results in conventional and navigated total knee arthroplasty, Clin Orthop Relat Res, 457:156-62, 2007.

[6] Bourne RB, et al. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res, 468(1):57-63, 2010.

[7] Scott CE, et al. Predicting dissatisfaction following total knee replacement: a prospective study of 1217 patients, J Bone Joint Surg Br, 92(9):1253–8, 2010.

[8] Jeffery RS, et al. Coronal alignment after total knee replacement, J Bone Joint Surg Br, 73(5): 709-14, 1991.

[9] Ritter A, et al. Postoperative alignment of total knee replacement: its effect on survival. Clin Orthop Relat Res. 1994;(299):153-6.

[10] Wasielewski RC, et al. Wear patterns on retrieved polyethylene tibial inserts and their relationship to technical considerations during total knee arthroplasty. Clin Orthop Relat Res. 1994;(299):31-43.

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DISCLOSURESLA and YD are employees of Exactech Inc; AJ, CH, and FB are employees of Blue Ortho; DL is a paid consultant of Exactech Inc.

Figure 1: A) tibial and B) femoral deviations (planned vs checked).

Figure 1: Distribution of the gap asymmetry in A) coronal plane, B) sagittal plane, and C) resection depth based on available TKA cases with gap measurement records.



Figure 1: Distribution of the gap asymmetry in A) coronal plane, B) sagittal plane, and C) resection depth based on available TKA cases with gap measurement records.





COMPUTER-ASSISTED TOTAL KNEE ARTHROPLASTY: IMPACT OF SURGEON EXPERIENCE ON THE ABILITY TO ACHIEVE SURGICAL RESECTION GOALS Yifei Dai PhD1*, Laurent Angibaud BS1, Amaury Jung BS2, Cyril Hamad BS2, Fabrice Bertrand BS2 1*Exactech Inc, Gainesville, FL, 32653, USA, [email protected] 2 Blue Ortho, La Tronche, 38700, FR

INTRODUCTION Accurate positioning of the knee prosthesis is critical for the success of total knee arthroplasty (TKA) [1]. TKAs performed using conventional instruments highly rely on surgeon’s experience and skill level. Studies have reported that only 70-80% of the TKA cases using conventional instruments can achieve satisfactory lower limb alignment (within ±3° of varus/valgus relative to the mechanical axis) [2,3], which may be one of the major contribution factors to the fact that up to 20% of patients remain dissatisfied with the results of the surgery [4]. Computer-assisted orthopaedic surgery (CAOS) has been shown to offer increased accuracy and precision to the bony resections compared to the conventional techniques [5]. As the early adopters champion the technology, reservation may exist among new CAOS users of (novice surgeons) regarding the ability of achieving the same results as the experienced surgeons can produce. To date, limited retrospective review has been done on the differences between experience users and novice user of a specific CAOS system based on a database of surgical reports. The purpose of this study was to investigate if there are immediate benefits in the accuracy and precision of achieving surgical goals for the novice surgeons, as compared to the experienced surgeons, by using a contemporary CAOS system.

MATERIALS AND METHODS Two groups of surgeons were randomly selected from a record retaining database for the TKA surgeries performed between October 2012 and January 2016 using a contemporary CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR). The records did not pertain any information related to the patients. The first group (novice users) included 7 surgeons, who had no navigation experience prior to the adoption of the CAOS system studied and performed equal or less than 20 CAOS TKAs in their practice. To investigate the intra-group variation in the novice group, the “novice group” was further divided into established surgeons with extensive experience in conventional TKA (novice-senior group), and junior surgeons who were less experienced (novice-junior group). The second group contained 6 surgeons (experiences users), each used the CAOS system for more than 150 TKAs. All the surgeries from the first group were included in the study, annotated as the “novice group” (86 cases). The most recent 20 cases from each surgeon in the second group were collected as the “experienced group” (120 cases). The following surgical parameters were investigated in both groups: 1) planned resection, resection goals defined by the surgeon prior to the bone cuts; 2) checked resection, digitization of the realized resection surfaces, obtained by manually pressing an instrumented checker onto the bony cuts. Due to that anterior, posterior and facet cuts of the femur were all based on the distal resection, only the distal resection was evaluated for the femur.

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Table 1. Deviation between planned and achieved resections for each surgeon group.

Figure 1. Distribution of the deviations in experienced and novice groups. The percentages of bones that fell in

optimal and acceptable resection categories were also presented for each group.

Deviations in the resection parameters were quantified for both tibia and femur (planned vs checked). The results were compared within the novice group (novice-senior vs novice-junior), as well as between the novice and experience groups (ANOVA). In addition, knees with optimal resection (<2°/mm in deviation, as greater differences may clinically alter the joint mechanics [6]) and acceptable resection (<3°/mm in deviation, as commonly adopted in the existing studies [2,3]) were identified. Statistical significance was defined as p<0.05.

RESULTS A summary of the deviations between the planned and achieved resections for is presented in Table 1. No statistical differences were found between the senior and the junior surgeons in the novice group. Similarly, no differences were found between the experienced group and novice group, except for that the cases in the novice group tended to resect slightly more bone in the tibia (p < 0.01), and had slightly larger standard deviations compared to the experienced group. The experienced and novice groups had comparable, high percentages of the knees in both the optimal and acceptable categories (Fig 1).

DISCUSSION This study demonstrated that regardless of the surgeon’s experience with TKA in general, new adoption of the CAOS system investigated can immediately benefit the accuracy and precision of the bony resections at a comparable level with experience CAOS users. Although significant difference was found between novice and experienced groups in tibial resection depth, the difference in was too small to be clinical relevant (difference in means = 0.57mm). The CAOS system offers substantial reduction of the outliers compared to TKAs performed with conventional instruments [4]. The findings aligned with a smaller scope study including multiple CAOS systems [7].

REFERENCES [1] Fehring TK, Odum et al. Early failures in total knee arthroplasty. Clin Orthop Relat Res, (392):315-8, 2001.

[2] Ensini A, et al. Alignments and clinical results in conventional and navigated total knee arthroplasty, Clin Orthop Relat Res, 457:156-62, 2007.

[3] Hetaimish BM, et al. Meta-analysis of navigation vs conventional total knee arthroplasty. J Arthroplasty, 27(6):1177-82, 2012.

[4] Scott CE, et al. Predicting dissatisfaction following total knee replacement: a prospective study of 1217 patients, J Bone Joint Surg Br, 92(9):1253–8, 2010.

[5] Sparmann M, et al. Positioning of total knee arthroplasty with and without navigation support: a prospective, randomised study. J Bone Joint Surg Br, 85(6):830-5, 2003.

[6] Walker PS, et al. Effects of surgical variables in balancing of total knee replacements using an instrumented tibial trial. Knee, 21(1):156-61, 2014.

[7] Ballas R, et al. Computer-assisted total knee arthroplasty: impact of the surgeon's experience on the component placement, Arch Orthop Trauma Surg, 133(3):397-403, 2013.

DISCLOSURES

LA and YD are employees of Exactech Inc; AJ, CH, and FB are employees of Blue Ortho.

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Computer-Assisted Surgery Provides an Effective and Accurate Tool for Naturally Aligned Total Knee Arthroplasty

Yifei Dai1, Matteo Petrera2, Laurent Angibaud1, Pasquale Petrera3

1Exactech Inc, Gainesville, FL, USA, 2N/A, Salisbury, MD, 3Peninsula Orthopaedic Associates, Salisbury, MD

Disclosures: Laurent Angibaud and Yifei Dai (3A,4 Exactech Inc), Pasquale Petrera (3B-Exactech Inc), Matteo Petrera (N)

Introduction:The natural alignment of the healthy knees demonstrates constitutional varus in up to 32% of adult men and 17% of adult women [1]. Some authors have proposed that restoration of a slight varus alignment in varus knees during total knee arthroplasty (TKA) may offer benefits to better postoperative natural kinematics [2,3]. However in reality, it is a paramount technical challenge to determine and achieve a natural alignment using conventional TKA instruments with sufficient efficiency and accuracy. With the recent technical advance of computer-assisted orthopaedic surgery (CAOS), achieving natural alignment may now be feasible. This study sought to demonstrate and evaluate a computer-assisted surgical technique aiming to restore individual natural alignment inthe varus knees.

Materials and Methods:Thirty-four varus (>3°) knees without significant soft-tissue deficiency, including 17 males (age 72.7±7.2yrs, height 176.6±7.4cm, BMI 32.1±4.4) and 17 females (age 67.9±6.3yrs, height 159.9±7.9cm, BMI 33.8±5.5) were studied. The knees were selected from the primary posterior stabilized TKAs performedby the surgeon author (PP) using a CAOS system (ExactechGPS®, Blue-Ortho, Grenoble, FR). This selection was carried out by assessing the varus/valgus deformity (preoperative deformity) using the CAOS system at full extension in supine position after the arthrotomy. Before any bony resection, the surgeon applied a valgus stress at full extension to measure the maximum alignment correction allowed as guided by the soft-tissue (i.e. the medial collateral ligament). From this measurement, a natural alignment target was set in the CAOS system to guide the proximal tibia resection for each patient, which was allowed to have some residual varus as dictated by the soft tissue (distal femur resected to neutral relative to mechanical axis). The TKA was then completed using a tensor facilitated gap balancing technique (in 90° flexion) guided by the CAOS system. The final achieved alignment was checked using the CAOS system (achieved alignment). The preoperative varus deformity, the natural alignment target, and the achieved alignment were compared and analyzed, with statistical significance defined as p<0.05.

Results:The preoperative varus deformity, the natural alignment target, the achieved alignment, and surgical errors in alignment are presented in Table 1. Significant corrections were applied to the varus knees investigated (achieved alignment vs. preoperative deformity, ANOVA p values < 0.01, Figure 1). The natural alignment target in the male knees was on average 1.6° more varus than that in the female knees (ANOVA p=0.03). No differences were found between natural alignment target and achieved alignment (paired t-test p>0.2). Both the natural alignment target and the achieved alignment were close (<1°) to the reported constitutional varus angle for both genders [1]. The mean error between the natural alignment target and the achieved alignment was less than 0.5°for both genders and pooled data.

Discussion:This study demonstrated the effectiveness and accuracy of using a CAOS system to assist achieving natural alignment in the varus knees. The use of the CAOS system greatly facilitated the surgical technique by offering the ability to quantify the alignment target, provide guidance to bony resection, and assess the accuracy of the achieved alignment. Although this is a CAOS procedure with a patient-specific surgical goal, the surgical time was comparable to standard mechanical alignment surgery using conventional instruments (reported in a separate study [4]). The study showed that a CAOS system can be of great value in achieving the patient-specific surgical goal defined intraoperatively by the surgeons.

Significance:Computer-assisted TKA surgery can help surgeons achieve patient-specific alignment goal with both efficiency and accuracy, which is not easily achievable by using conventional instrumentation.

References:[1] Bellemans J, et al. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res. 2012. 470(1):45-53; [2] Bellemans J. Neutral mechanical alignment: a requirement for successful TKA: opposes. Orthopedics. 2011. 34(9):e507-9; [2] Howell SM, et al. Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res. 2013. 471(3):1000-7; [4] Angibaud L, et al. ExactechGPS Guidance System Does Not Increase Operative Time When Compared to Conventionally Instrumented Total Knee Arthroplasty. ISTA 2015, Vienna, AT.


Computer-Assisted Surgery Provides an Effective and Accurate Tool for Naturally Aligned Total Knee Arthroplasty

Yifei Dai1, Matteo Petrera2, Laurent Angibaud1, Pasquale Petrera3

1Exactech Inc, Gainesville, FL, USA, 2N/A, Salisbury, MD, 3Peninsula Orthopaedic Associates, Salisbury, MD

Disclosures: Laurent Angibaud and Yifei Dai (3A,4 Exactech Inc), Pasquale Petrera (3B-Exactech Inc), Matteo Petrera (N)

Introduction:The natural alignment of the healthy knees demonstrates constitutional varus in up to 32% of adult men and 17% of adult women [1]. Some authors have proposed that restoration of a slight varus alignment in varus knees during total knee arthroplasty (TKA) may offer benefits to better postoperative natural kinematics [2,3]. However in reality, it is a paramount technical challenge to determine and achieve a natural alignment using conventional TKA instruments with sufficient efficiency and accuracy. With the recent technical advance of computer-assisted orthopaedic surgery (CAOS), achieving natural alignment may now be feasible. This study sought to demonstrate and evaluate a computer-assisted surgical technique aiming to restore individual natural alignment inthe varus knees.

Materials and Methods:Thirty-four varus (>3°) knees without significant soft-tissue deficiency, including 17 males (age 72.7±7.2yrs, height 176.6±7.4cm, BMI 32.1±4.4) and 17 females (age 67.9±6.3yrs, height 159.9±7.9cm, BMI 33.8±5.5) were studied. The knees were selected from the primary posterior stabilized TKAs performedby the surgeon author (PP) using a CAOS system (ExactechGPS®, Blue-Ortho, Grenoble, FR). This selection was carried out by assessing the varus/valgus deformity (preoperative deformity) using the CAOS system at full extension in supine position after the arthrotomy. Before any bony resection, the surgeon applied a valgus stress at full extension to measure the maximum alignment correction allowed as guided by the soft-tissue (i.e. the medial collateral ligament). From this measurement, a natural alignment target was set in the CAOS system to guide the proximal tibia resection for each patient, which was allowed to have some residual varus as dictated by the soft tissue (distal femur resected to neutral relative to mechanical axis). The TKA was then completed using a tensor facilitated gap balancing technique (in 90° flexion) guided by the CAOS system. The final achieved alignment was checked using the CAOS system (achieved alignment). The preoperative varus deformity, the natural alignment target, and the achieved alignment were compared and analyzed, with statistical significance defined as p<0.05.

Results:The preoperative varus deformity, the natural alignment target, the achieved alignment, and surgical errors in alignment are presented in Table 1. Significant corrections were applied to the varus knees investigated (achieved alignment vs. preoperative deformity, ANOVA p values < 0.01, Figure 1). The natural alignment target in the male knees was on average 1.6° more varus than that in the female knees (ANOVA p=0.03). No differences were found between natural alignment target and achieved alignment (paired t-test p>0.2). Both the natural alignment target and the achieved alignment were close (<1°) to the reported constitutional varus angle for both genders [1]. The mean error between the natural alignment target and the achieved alignment was less than 0.5°for both genders and pooled data.

Discussion:This study demonstrated the effectiveness and accuracy of using a CAOS system to assist achieving natural alignment in the varus knees. The use of the CAOS system greatly facilitated the surgical technique by offering the ability to quantify the alignment target, provide guidance to bony resection, and assess the accuracy of the achieved alignment. Although this is a CAOS procedure with a patient-specific surgical goal, the surgical time was comparable to standard mechanical alignment surgery using conventional instruments (reported in a separate study [4]). The study showed that a CAOS system can be of great value in achieving the patient-specific surgical goal defined intraoperatively by the surgeons.

Significance:Computer-assisted TKA surgery can help surgeons achieve patient-specific alignment goal with both efficiency and accuracy, which is not easily achievable by using conventional instrumentation.

References:[1] Bellemans J, et al. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res. 2012. 470(1):45-53; [2] Bellemans J. Neutral mechanical alignment: a requirement for successful TKA: opposes. Orthopedics. 2011. 34(9):e507-9; [2] Howell SM, et al. Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res. 2013. 471(3):1000-7; [4] Angibaud L, et al. ExactechGPS Guidance System Does Not Increase Operative Time When Compared to Conventionally Instrumented Total Knee Arthroplasty. ISTA 2015, Vienna, AT.








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Evaluation of Anteroposterior Kinematics during Cruciate-‐Retaining Total Knee Arthroplasty

Yifei Dai1, Laurent Angibaud1, Jean-Yves Jenny2, Michael B Cross3, Amaury Jung4, Cyril Hamad4

1Exactech Inc, Gainesville, FL, USA, 2Hôpitaux Universitaires de Strasbourg, Illkirch, FR, 3Hospital for Special Surgery, New York, NY, USA, 4Blue Ortho, La Tronche, FR

Disclosures: Laurent Angibaud and Yifei Dai (3A,4 Exactech Inc), Michael B Cross (1,3B,5-Smith and Nephew PLC, 3B-Exactech Inc, LinkBio Corp, Intellijoint Surgical Inc), Jean-Yves Jenny (1-Aesculap Inc, 3B-FH Orthopedics Inc, Exactech Inc), Amaury Jung and Cyril Hamad (3A Blue Ortho) Introduction: Paradoxical motion, characterized as non-physiological anterior sliding of the distal femur relative to the proximal tibia, is a unique phenomenon in the anteroposterior (AP) kinematics of cruciate-retaining total knee arthroplasty (CR TKA) that is prevalent in as many as 83% of the CR TKA knees. Besides altering normal AP knee kinematics, this undesirable motion can limit postoperative range of motion, increase wear of the polyethylene insert, and elevate strain in the surrounding soft tissues. Although postoperative tibiofemoral AP displacement has been evaluated in various CR designs, the evaluations were based on kinematic testing of a single component placement on each knee specimen. Surgical parameters, such as the reconstructed posterior tibial slope (PTS), were usually overlooked during the evaluation. The purpose of this study was to investigate the AP kinematics of a CR TKA design in combination with variations in PTS. Materials and Methods: CR TKAs were performed on six cadaveric knees (fresh frozen, non-arthritic, PCL presumably intact) using a CAOS system. The implanted tibial baseplate was specifically designed with a mechanism to precisely and easily modify the PTS without potential damages to the soft-tissue envelope. After implantation at each of the 4 PTSs (10°, 7°, 4°, and 1°), knee kinematics was measured by the CAOS system through passive range of motion (ROM) tests. Each measurement was performed with a closed arthrotomy (patella reduced in the trochlea groove) and repeated 3 times. The AP displacement of the medial and lateral contact locations between the femoral component condyles and the tibial component were tracked referencing the center of the proximal tibia. The average AP displacements was evaluated from 0° to 90° flexion to identify any paradoxical motion and compared between PTSs. Statistical analysis of the data was performed by sampling at every 5° from 20° to 90° of flexion, with significance defined as p < 0.05. Results: No paradoxical sliding was observed for all 4 PTSs (Fig. 1). Across the 0° to 90° flexion range, all 4 PTS exhibited a physiological rollback pattern. No significant differences were found between the 4 PTS groups in both medial (p ≥ 0.40) and lateral (p ≥ 0.38) AP displacement. Discussion: This study utilized a CAOS system to quantitatively evaluate the AP kinematics of a CR TKA design. Compared to other designs that were reported to have paradoxical motion, the data demonstrated that regardless to the PTS selected for the CR TKA, the design investigated exhibits physiological and non-paradoxical AP motion during mid-flexion. This method can be expended to various surgical parameters to investigate their impact on the TKA kinematics.

Figure 1. Average AP displacement (n=6) for PTSs of A) 1°, B) 4°, C) 7°, and D) 10°.

ExactechGPS Guidance System Does Not Increase Operative Time When Compared to Conventionally Instrumented Total Knee Arthroplasty

Pasquale Petrera MD; Xeve Silver MS; Laurent Angibaud BS

Introduction

Computer assisted orthopedic surgery (CAOS) improves implant alignment in TKA [1,2]. However, one perceived drawback for its application is the increased surgical time compared to the use of standard mechanical instrumentation. This study compared the time efficiency between a next generation CAOS system (ExactechGPS®, Blue-Ortho, Grenoble, FR) and conventional instrumentations, and assessed the impact of surgeon experience on the efficiency.

Method

Surgical time was retrospectively reviewed on sixty-three primary TKAs performed by a board-certified orthopedic surgeon (PP) using Optetrak Logic® PS knee system (Exactech, Gainsville, FL), grouped as 1) Group I (control): 21 TKAs using conventional mechanical instruments; 2) Group II: 21 TKAs performed with early experiences using ExactechGPS; and 3) Group III: 21 TKAs performed with advanced experiences using ExactechGPS. Patient condition (age, BMI, gender, etc.), surgical technique (excluding the use of the guidance system), and post-operative guidelines were similar across the three groups. No cases were lost and no patient had any intra-operative complications. Surgical time was compared across the three groups (significance defined as p<0.05).

Results

A summary of the surgical time is presented in Table 1. Compared to the TKAs using conventional mechanical instruments, the average surgical time for the TKAs performed with early ExactechGPS experiences was 7 minutes longer. However, with advanced ExactechGPS experience, the average surgical time decreased to 2 minutes less than the time required by using conventional mechanical instruments. Furthermore, TKAs with advanced ExactechGPS experience exhibited the least variability (standard deviation) among the three groups. None of the differences were significant (p>0.20).

Discussion

The results demonstrated that with ExactechGPS, there was no significant difference in TKA surgical time compared to the conventional instrumentation. Nevertheless, once the initial learning curve is reached, the guidance system generally decreases the surgery time compared to conventional mechanical instrumentation.

In contrast to data reported on traditional navigation systems [3-5], the comparable (with conventional mechanical instrumentation) efficiency reported in this study may be contributed to the unique features of the ExactechGPS system compared to traditional CAOS technologies, such as indication for use inside the sterile field, blood occlusion-resistant tracker design, customizable operative technique according to

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the surgeon’s preference, and overall compact and reduced number of instruments. The system may provide an advantageous solution for reducing surgical cost and improving clinical outcomes.

References

1. Jenny JY, Clemens U, Kohler S, Kiefer H, Konermann W, Miehlke RK, Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case-control study of 235 cases compared with 235 conventionally implanted prostheses. J Arthroplasty, 20(7), pp: 832-839, 2005.

2. Haaker RG, Stockheim M, Kamp M, Proff G, Breitenfelder J, Ottersbach A, Computer-assisted navigation increases precision of component placement in total knee arthroplasty, Clin Orthop Relat Res 433, pp:152-159, 2005.

3. Sisten RA, Giori NJ, Goodman SB, Delp SL, Surgical navigation for total knee arthroplasty: a perspective, J Biomech, 40(4), pp: 728-735, 2007.

4. Saragaglia D, Picard F, Chaussard C, Montbarbon E, Leitner F, Cinguin P, Computed assisted knee arthroplasty: comparison with a conventional procedure. Results of 50 cases in a prospective randomized study, Rev Chir Orthop Reparatrice Appar Mot, 87, pp :18-28,2001.

5. Chauhan SK, Scott RG, Breidahl W, Beaver RJ, Computer-assisted knee arthropolasty versus a conventional jig-based technique: a randomized, prospective trial, J Bone Joint Surg Br, 86, pp :372-377,2004.

Table 1. Surgical time for each TKA group.

A Review Paper

32 A Supplement to The American Journal of Orthopedics®

AbstractOur aim in this article is to describe the impact that navi-gation technology has had on the market share of a com-munity hospital and, specifically, to determine whether a high-volume surgeon using these technologies actually costs the hospital more than other surgeons at the same hospital and more than national means. In addition, we develop a comparable cost-effectiveness model for robotic technology in unicompartmental knee arthro-plasty to demonstrate the potential cost-effectiveness at the same hospital.

Introducing new technologies (eg, computer navigation and, more recently, robotics) into the operating room has an undeniable initial capital equipment cost or lease (approximately $150,000-$300,000 for navigation, up to

$800,000 for robotics), a per-case disposable cost, and opera-tional costs.1 Opponents of these technologies argue that these incremental costs are unjustified or unnecessary. Proponents of these technologies have demonstrated that, if the technologies are able to lower revision rates to a specific level, then they may be cost-effective.2,3 It has been predicted that, after 10 years of computer navigation use in total knee arthroplasty (TKA), revision rates would have dropped by 1.6%, resulting in a relative cost-per-case reduction of $1,100 for computer naviga-tion ($13,200) compared with conventional knee replacement ($14,300).4 Long-term data regarding whether navigation prolongs implant life or decreases costly revisions are limited

because of the relatively recent and slow implementation of imageless systems. Study results have shown that there is an incremental cost of $871 more per case when using com-puter navigation versus conventional guides.2 As the volume of arthroplasties increases, the cost lessens a mean of $463 per primary TKA, making computer navigation more cost-effective. Navigation can lengthen operation times by 11 to 18 minutes, possibly more during the learning curve.5 Surgeons who have trained residents assisting in pin placement have demonstrated decreased overall operating time.6

Cost-effectiveness data from actual use of either naviga-tion or robotic technology are scant. Most authors use sta-tistical models or hypothetical scenarios. Dong and Buxton7 addressed cost-effectiveness in navigated TKAs, but imped-ing factors caused their model to overestimate, by $430/case, the cost of computer-assisted surgery (CAS). Navigation costs can be justified if intraoperative and postoperative complica-tions can be reduced through use of navigation. Navigation has demonstrated both decreased blood loss8 and cerebro-vascular emboli,9 thus providing cost savings associated with less transfusion, less unnecessary and wasted autologous blood donation, and decreased cost of hospitalization.

Lack of data has contributed to the slow adoption of these precision technologies. Only 3% to 5% of knee replacements involve navigation technology, despite some evidence that navigation improves radiographic alignment in TKA.2,5,10-19 Navigation is advocated particularly when there are complex posttraumatic deformities or when hardware makes use of intramedullary instruments impossible or impractical.6 Diminishing reimbursements have contributed to resistance to adoption of computer navigation technology. Rising costs of implants (up to 50% of the expense of joint replacement service lines), coupled with decreased margins, payer mix, and lower reimbursement, influence decision makers (hospi-tals, surgeons) when they consider adopting new technology. Category III Current Procedural Terminology (CPT) tempo-

Technology and Cost-Effectiveness in Knee Arthroplasty: Computer Navigation and RoboticsMichael L. Swank, MD, Martha Alkire, CNP, Michael Conditt, PhD, and Jess H. Lonner, MD

Dr. Swank is Director, Joint Replacement Program, Jewish Hospital, Cincinnati, Ohio, and President, Cincinnati Orthopaedic Research Institute, Cincinnati, Ohio.Ms. Alkire is Clinical Nurse Practitioner, Cincinnati Orthopaedic Research Institute, Cincinnati, Ohio.Dr. Conditt is Director of Clinical Research, MAKO Surgical, Fort Lauderdale, Florida.Dr. Lonner is Director, Knee Replacement Surgery, Pennsylvania Hospital, Philadelphia, Pennsylvania, and Director, Philadelphia Center for Minimally Invasive Knee Surgery, Philadelphia, Pennsylvania.

Address correspondence to: Michael L. Swank, MD, Cincinnati Orthopaedic Research Institute, 9825 Kenwood Road, Suite 200, Cincinnati, OH 45242 (e-mail, [email protected]).

Am J Orthop. 2009;38(2 suppl):32-36. Copyright, Quadrant HealthCom Inc. 2009. All rights reserved.

“...if the technologies are able to lower revision rates to a specific level, then they may be cost-effective.”

TECHNOLOGY AND COST-EFFECTIVENESS IN KNEE ARTHROPLASTY: COMPUTER NAVIGATION AND ROBOTICS AM J ORTHOP. 2009;38(2 SUPPL):32-36.

Michael L. Swank, M.D; Martha Alkire, CNP, Michael Conditt, PhD, and Jess H. Lonner, MD; Am J

Orthop. 2009;38(2suppl):32-36.

PubMed ID: 19340382

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Title Tibial and femoral stem extension fatigue performance with and without LPB treatment. Background Modular total knee arthroplasty (TKA) systems today provide surgical flexibility that allows a surgeon to optimize implant configurations for a variety of patients in order to restore knee function and stability. As the demands for implant performance increase from an ever broadening patient demographic,1,2 advanced materials and manufacturing techniques may hold the key towards the development of implants with greater long term efficacy and patient satisfaction. Towards this end, Exactech has sought novel methods to improve the fatigue performance of tibial and femoral stem extensions used in its newest revision system, Logic CC. Low Plasticity Burnishing (LPB) is a process by which a smooth free-rolling spherical ball is moved across a metallic surface under a sufficiently high force to induce plastic deformation, thereby creating a compressive outer layer of residual stress.3 Initially used in aerospace, LPB processing has been shown to significantly improve surface finish, improve fatigue strength through the retardation of fatigue crack nucleation, and reduce susceptibility to corrosion in titanium.4,5 For these reasons, LPB was investigated as a technology that would further improve from the existing tibial and femoral stem extension fatigue performance. To this end, an extreme loading scenario under lab testing environment was used to compare the fatigue performance and endurance limit of tibial stem extensions with and without LPB processing. Question/Purposes Will LPB technology applied to tibial and femoral stem extensions provide an improvement in fatigue performance that will meet the growing demands of an ever evolving revision TKA patient cohort? Methods Two configurations of the same Exactech design were chosen to evaluate the effect of LPB on stem extension fatigue performance; consisting of a LPB treated and untreated titanium (Ti) stem extension paired with cobalt chromium (CoCr) tibial tray. Five samples were tested of each configuration, with each sample receiving an individual test load magnitude, respectively (Table 1). Each test was set up by constraining the tibial tray to the base of the load frame, with load applied at a distance of 4.65 cm, measured from the bottom surface of the tibial tray (Figure 1). A competitive design configuration with identical modular locking mechanisms, consisted of Ti tibial stem extension without LPB treatment and Ti tibial tray, was tested to compare with the fatigue performance of the two Exactech design configurations.

Figure 1. Photograph demonstrating the test setup. The tibial tray potted in polymethyl-methacrylate was fixed within a vise while a force was cyclically applied perpendicular to the long axis of the stem extension 4.65cm from the most distal point of the tibial tray.

Table 1. Details of the five loading magnitudes. Load Magnitude Mean (N) Amplitude (N) Peak Moment (Nm) Peak Force (N) 1 935 765 79 1700 2 1101 901 93 2002 3 1211 991 102 2202 4 1332 1090 113 2422 5 1465 1199 124 2664

The forces were adapted from a previous stem extension fatigue test6 and were expected to encompass cycle to failure values between 10 million and 1,000. Force was applied sinusoidally at a frequency of 3Hz. All tests were discontinued if 10 million cycles (Mc) had been reached or taper junction failure occurred. Failure was indicated by relative rotation between the stem extension and tibial tray, cracking at the taper junction, or inability of the stem extension to resist loading. Results LPB Untreated Samples; CoCr Tray – Ti Stem Extension Cycles-to-failure for each test sample are provided in Figure 2 and Table 2. All samples except Sample 5, which underwent the highest loading magnitude, had fracture sites located within the stem extension-tibial tray junction (Figure 3). Sample 5 fractured approximately 15mm from the distal surface of the tibial tray (Figure 4), the cause could not be determined.

Table 2. Fatigue performance for individual test specimens.

Sample # Peak Cyclic Load (N) Cycles Completed Before Failure Competitive-LPB Exactech+LPB Exactech-LPB

1 1700 *16,005 §n/a 226,679 2 2002 n/a †10,000,000 144,718 3 2202 n/a 4,050,910 94,538 4 2422 n/a 126,255 39,482 5 2664 n/a 41,593 19,643

*16,005 represents the average of two samples. †Sample did not fail. § Was not tested as Sample 2 was evaluated at a higher load and successfully completed 10 Mc.

LPB Treated Samples; CoCr Tray – Ti Stem Extension The sample tested at the second to lowest loading magnitude (peak cyclic force of 2002 N) reached the required 10 Mc without failing. For this reason, it was unnecessary to test a sample at the lowest load, as its cycle count was expected to exceed 10 Mc as well. Cycles-to-failure for each tested sample are reported in Figure 2 and Table 2. All failed samples fractured at the stem extension, with the fracture initiated within the stem extension-tibial tray junction (Figure 3).

Competitive Samples; Ti Tray – Ti Stem Extension, LPB Untreated Samples (N=2) immediately failed at the lowest force magnitude; therefore it was not necessary to evaluate additional samples at the higher loading magnitudes. Cycles-to-failure for the competitive samples are reported in Figure 2 and Table 2. Both samples fractured at the stem extension, with the fracture initiated within the stem extension-tibial tray junction. Previous results have indicated that a Ti-Ti junction has better fatigue performance than an otherwise identical CoCr-Ti junction. The results herein contradicted the initial prediction that the competitive samples would outperform the untreated CoCr-Ti test samples.

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Figure 2. Force versus cycles before failure are plotted for the treated and untreated CoCr tibial tray and titanium stem extension assemblies, and competitive samples.

Figure 3. Representative images of a failed stem extension. Fracture initiation occurs at the top, which was the location of highest tensile stress.

Figure 4. Photograph of unusual point of failure for Sample 5. This failure mode only occurred at the highest load in the series and was not reproduced on other tests. The remaining samples failed in the manner shown in Figure 3.

Figure 5. Photograph of the competitive stem extension samples and tibial tray.

Conclusions The results suggest that LPB surface treatment substantially improves the fatigue performance of the CoCr tibial tray and stem extension configuration investigated. This may suggest that under extreme loading conditions, such that the stem extension experiences high transverse forces relative to the tibial tray, a stem treated with LPB would be less prone to fracture over an untreated counterpart. In summary, LPB treatment has demonstrated an improvement of the fatigue performance of modular stem-taper constructs in Logic CC design, which may better address the increased demand by a younger, more active patient population. References [1] Namba, Robert S., Liz Paxton, Donald C. Fithian, and Mary Lou Stone. "Obesity and perioperative morbidity in

total hip and total knee arthroplasty patients." The Journal of arthroplasty 20 (2005): 46-50. [2] Kurtz, Steven M., Edmund Lau, Kevin Ong, Ke Zhao, Michael Kelly, and Kevin J. Bozic. "Future young

patient demand for primary and revision joint replacement: national projections from 2010 to 2030." Clinical Orthopaedics and Related Research® 467, no. 10 (2009): 2606-2612.

[3] U.S. Patent 5,826,453 (Oct. 1998), other patents pending. [4] Prevéy, Paul S., D. J. Hornbach, T. L. Jacobs, and Ravi Ravindranath. Improved damage tolerance in titanium

alloy fan blades with low plasticity burnishing. No. N68335-01-C-0274. LAMBDA RESEARCH CINCINNATI OH, 2002.

[5] Prevéy, Paul S., and John Cammett. "Low cost corrosion damage mitigation and improved fatigue performance

of low plasticity burnished 7075-T6." Journal of Materials Engineering and Performance10, no. 5 (2001): 548-555.

[6] Yarger, CW. Research and development report for vendor approval testing of stem extensions. Exactech

Technical Report, TR-2002-004.

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INNOVATIONS | A CLINICAL EXCHANGE ON ADVANCES IN ORTHOPAEDICS34

A SURGEON’S PERSPECTIVE ON WHY NAVIGATION IS IMPORTANT IN REVISION TOTAL KNEE ARTHROPLASTY

James Huddleston, MD Stanford University Medical

Center

Navigation, or computer-assisted surgery, has been around for many years. Many

of us have had experience with at least one of the major systems on the market.

Most recently, I have been using ExactechGPS® for my primary TKA procedures.

Personally, I have had great success with the system and believe that my patients

have benefited accordingly. So when Exactech asked me to be a part of the team to

design their new revision knee system, Optetrak Logic® CC, and they informed me

that it included an opportunity to develop the first-of-its-kind application to use the

ExactechGPS system for revision procedures (rTKA), I was intrigued and ultimately

decided to accept the opportunity.

In my career as an orthopedic surgeon, I have performed 750 revision TKAs using

most of the major revision knee systems on the market. The majority of these sys-

tems had room for improvement. I knew there was an opportunity to create a state-

of-the-art system that uses computer-assisted surgery to achieve optimal outcomes

in the revision setting. Before I began to think through inputs on how the revision

platform for ExactechGPS could be beneficial to surgeons and patients, I knew that

it would be helpful to review data on how computer-assisted surgery is being used

in the primary knee setting.

During this journey, I realized that most orthopedic surgeons use computer-assist-

ed surgery to achieve better alignment, to be faster in the O.R., to have an overall

reduction in instrumentation, to avoid violating the IM canal and be able to access

pre and post-op kinematics. For the most part, the majority of these are achieved

through the use of computer-assisted surgery in TKA. In fact, one of the most

compelling pieces of literature I discovered came out of the 2013 Australian Ortho-

paedic Association National Joint Replacement Registry. These data showed that

when using navigation, there was a 20 percent reduction in the revision burden in

patients 65 years of age and younger.1 Additionally, the research highlighted that in

cases where aseptic rTKA was necessary, the primary cause was mechanical loos-

ening of the prosthetic joint (American Joint Replacement Registry & California Joint

Replacement Registry 2014).2 Another study “The Epidemiology of Revision Total

Knee Arthroplasty in the United States” found that out of 60,355 knees, 16 percent

failed due to mechanical loosening.3 Adding to the issue of loosening, Sharkey et

al. determined that 55.6 percent of revisions were performed less than two years

October 13-14 | Advanced Surgical Solutions for Shoulder, Hip and Knee Arthroplasty | San Diego, Calif.

www.exac.com/courses

COMMENTARY

VOLUME 2 • ISSUE 2 | 2016 35

after the initial operation.4 These data led me to believe there

is a clinical need for computer-assisted surgery in the revision

setting. What remains to be seen is if the use of navigation

will consistently yield better patient-reported outcomes in the

revision setting. Our hypothesis is that we will see improve-

ments in rTKA, based on the success of navigation in the pri-

mary setting.

With the conclusion that computer-assisted surgery for rTKA

was something we wanted to continue developing, we dis-

cussed features and benefits required to: 1) assist with

adoption of the technology and 2) to offer an improvement

in how revision procedures are performed. We decided to

focus on three key goals: 1) increasing the number of ortho-

pedic surgeons performing rTKA procedures, 2) making rTKA

procedures easier and more reproducible, and 3) collecting

data to see if the use of navigation in the revision setting will

yield clinical benefits. Because the number of revision knees

in the United States is expected to increase, it was important

to the team that the ExactechGPS revision application make

it easier for surgeons to perform rTKA procedures without

years of revision experience. This goal has been achieved

by developing a system that conducts acquisitions from the

previously implanted primary knee components, which allows

us as surgeons to easily document why it was sub-optimal.

A key feature of the revision application is the ability for the

surgeon to align with either the mechanical or anatomical axis

to produce the desired alignment. Overall, I believe the Exact-

echGPS revision platform should make revisions easier and

more efficient with improved functional outcomes. •

REFERENCES

1. Australian Orthopaedic Association, National Joint Replace-ment Registry, Annual Report 2013 – Hip and Knee Arthroplasty.

2. American Joint Replacement Registry and California Joint Re-placement Registry, Annual Report 2014

3. Bozic KJ, Kurtz SM, Lau E, Ong K, Chiu V, Vail TP, Rubash HE, Berry DJ. The epidemiology of revision total knee arthroplasty in the United States. Clin Orthop Relat Res. 2010 Jan;468(1):45-51. doi: 10.1007/s11999-009-0945-0. Epub 2009 Jun 25.

4. Sharkey PF, Hozack WJ, Rothman RH, Shastris, Jacoby SM. Insall Award paper. Why are total knees failing today? Clin Orthop Relat Res. 2002 Nov;(404):7-13.

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FEATURE ARTICLE

EARLY RESULTS OF A NEW REVISION TOTAL KNEE ARTHROPLASTY SYSTEM USED IN THE STAGED TREATMENT FOR CHRONIC PERIPROSTHETIC INFECTION

Daniel C. Allison, MD Cedars-Sinai Medical Center

INTRODUCTION

Periprosthetic infection is a devastating complication that complicates approxi-

mately 1 percent of primary total knee arthroplasties (TKA).1 In chronic cases, the

condition often requires implant removal with subsequent delayed reimplantation,

to offer the best chance at remission of infection.2 Extensive bone loss often oc-

curs in these settings, as a consequence of the infection itself, the removal of

implants, the initial debridement, from erosions caused by an unstable cement

spacer, or combinations thereof. In addition to bone deficiencies, soft tissue com-

promise and loss also frequents these conditions, for similar reasons. To minimize

and address the bone and soft tissue deficits at the time of reimplantation in these

challenging cases, a robust, versatile, and complete instrument and implant sys-

tem remains an essential part of the revision knee surgeon’s arsenal.

We report the early results of a small case series of a new condylar constrained

revision total knee replacement system (Optetrak Logic® CC, Exactech, Inc. [Ga-

niesville, FL) used in the staged treatment of chronic periprosthetic infection. The

system contains advances on both the instrument and implant sides, which may

be beneficial in these difficult cases.

MATERIALS AND METHODS

The first seven periprosthetic infection cases using the new Optetrak Logic CC

system performed by a single surgeon (Daniel C. Allison, MD) were restrospec-

tively reviewed. All cases involved the treatment of chronic periprosthetic infec-

tion, as diagnosed by MSIS criteria.3 All cases were initially treated with implant

removal, debridement, and articulating antibiotic cement spacer placement. In one

case, the patient was referred with a previous antibiotic spacer placed by another

surgeon, with persistent periprosthetic infection and severe instability (Case 2). In

another case, the antibiotic cement spacer was placed three years previously at an

VOLUME 2 • ISSUE 2 | 2016 25

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outside hospital (Case 4). In the remainder of cases, the initial implant removal

and antibiotic spacer placement was performed by the final treating surgeon

(Daniel C. Allison, MD). The decision to proceed with total knee arthroplasty

reimplantation was based on clinical examination, serum ESR / CRP values,

joint aspiration cell count, intraoperative gross examination, and intraoperative

frozen section sampling. In all cases, low dose antibiotic (1gm vancomycin, 1.2

gm tobramycin per 40 gm PMMA) cement was used during reimplantation.

Early clinical and radiographic results were collected, and mean follow up was

14 weeks from reimplantation (range 4-17 weeks). There were no unplanned

readmissions or surgeries within 30 days, and all cases sustained remission of

infection during the follow up period.

CASE REPORTS

CASE 1

A 57 year-old African American female with persistent right total knee arthro-

plasty fibrosis, treated with previous open lysis of adhesions and tibial insert

exchange at an outside hospital, presented with persistent pain and severe

stiffness. Intraoperative frozen section revealed >10 WBC per high power field

(HPF) in > 5 HPFs. At the time of implant removal, no specialized extraction

instrumentation was used, and iatrogenic, complete, displaced fracture of the

posteromedial tibial plateau occurred. The condition was immediately treated

with titanium plate fixation, followed by articulating antibiotic spacer place-

ment, and the patient’s weight bearing was limited (Figure 1A, 1B). The frac-

ture healed, remission of infection was achieved, and the patient underwent

reimplantation with the Optetrak Logic CC revision system (Figure 1C, 1D). At

27 weeks follow up, she remains free of infection, is ambulating without assis-

tive devices, and knee motion ranges from 15° to 100° (a 65° improvement in

arc of motion compared to preoperatively).

BA C D

Figure 1.

39

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CASE 2

An 81 year-old morbidly obese Caucasian female with multiple medical prob-

lems was referred by a colleague for persistent methicillin sensitive S. Aureus

right knee periprosthetic infection, along with severe instability and extensor

mechanism dysfunction, status post previous implant removal and articulating

antibiotic spacer placement (Figure 2A, 2B). The patient was taken to surgery

for repeat debridement, antibiotic spacer exchange, and extensor mechanism

reconstruction (Figure 2C, 2D). After a postoperative course of IV antibiotics,

remission of infection was confirmed, and she underwent reimplantation,

using extensive augmentation on the tibial and femoral sides (Figure 2E, 2F).

Her severe instability was managed with soft tissue balancing and use of the

condylar constrained design. At 24 weeks follow up, she has no pain or insta-

bility, with 0 – 100° of knee flexion / extension, actively and passively.

B

F

A

E

C

D

Figure 2.

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CASE 3

A 52 year-old male presented one-year status post left total knee arthroplasty

with persistent left knee pain, drainage, and inability to bear weight (Figure 3A,

3B). The diagnosis of chronic periprosthetic infection was confirmed, and the

patient was taken to surgery. Removal of femoral and tibial components was

facilitated with a specialized Exactech extraction device (Figure 3C, 3D), and

an articulating antibiotic spacer was placed. Intra-operative cultures grew En-

terococcus sp. After six weeks of IV antibiotic therapy, remission of infection

was achieved, and the patient was taken for uneventful reimplantation (Figure

3E, 3F). A posterior stabilized constrained (PSC) insert was used, given the

patient’s competent collateral ligaments. At 13 weeks follow up, the patient is

well healed, free of infection, ambulates without assistive devices, with range

of motion from 0 – 110°.

ED F

BA C

Figure 3.

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CASE 4

This patient is a 57 year-old male with a history of incomplete spinal cord in-

jury resulting in partial hemiparesis of his right lower extremity. The patient

underwent prior total knee arthoplasty, which became infected, and was treat-

ed with implant removal and articulating antibiotic cement spacer placement

at an outside hospital three years prior to consultation. He presented to our

clinic for reimplantation, complaining of knee instability and pain (Figure 4A,

4B). Infection workup was negative, and the patient was taken for complex

reimplantation, with a kinematic rotating hinged knee prosthesis as a back up

implant option, given the extensive bone and soft tissue loss in the setting of

weakened dynamic stabilizers. Intra-operatively, accommodation of bone de-

fects, as well as achievement of balance and stability, was accomplished with

the Optetrak Logic CC system (Figure 4C, 4D), and hinged knee replacement

was not necessary. At 12 weeks follow up, the patient is well healed, ambula-

tory with no pain, with range of motion from 0 – 100°, actively and passively.

BA

C D

Figure 4.

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CASE 5

A 73 year-old male S/P total knee arthroplasty presented with persistent pain,

swelling, and drainage (Figures 5A, 5B). Evaluation revealed methicillin resis-

tant S. Aureus infection, and the patient was taken to surgery. His implants

were very well fixed, and safe removal was facilitated with the Exactech Acu-

Driver® pneumatic device to disrupt the cement-bone interface, followed by the

Exactech extraction instrumentation for removal (Figures 5C, 5D). The implants

were removed with relative ease and minimal bone loss (Figures 5E, 5F). After

remission of infection was confirmed, the patient underwent reimplantation

(Figures 5G, 5H). A PSC insert was used, since the patient’s collateral liga-

ments afforded natural articular stability. At nine weeks follow up, he is well

healed, with no evidence of infection, and a 0 -100° arc of motion.

BA C

D E

G

F

H

Figure 5.

43

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CASE 6

A 71 year-old female presented to our service status post implant removal and

antibiotic spacer placement with gastrocnemius rotational flap coverage at an

outside hospital, with loss of patellar tendon at time of initial debridement,

as well as failure of her original flap (Figures 6A, 6B). We took the patient for

repeat debridement with articulating antibiotic spacer exchange with recon-

struction of the patellar tendon with allogenic collagen matrix, followed by free

latissimus dorsi flap coverage by the plastic surgery service (Figure 6C). After

her IV antibiotic course, remission of infection was achieved, and the patient

was taken back to surgery for reimplantation. Intraoperative examination re-

vealed that her extensor mechanism remained intact (Figures 6D, 6E). At six

weeks follow up, she is well healed with no evidence of infection, with an

intact extensor mechanism, and ambulating with a front wheeled walker.

BA

E

C

D

Figure 6.

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CASE 7

An 80 year-old male on chronic high dose anticoagulation therapy presented

with chronic periprosthetic infection, secondary to Morganella morganii. The

patient was treated with implant removal and antibiotic spacer placement (Fig-

ure 7A, 7B) followed by staged reimplantation (Figures 7C, 7D). At the time of

reimplantation, gastrocnemius rotational flap coverage was performed by the

orthopedic service, in order to augment attenuated anteromedial soft tissues.

At four weeks follow up, the patient is well healed, with no evidence of infec-

tion, and ambulatory with a front wheeled walker.

BA

C D

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DISCUSSION

The treatment of chronic periprosthetic infection of the knee can be challeng-

ing, especially with regard to the extensive bone loss and soft tissue compro-

mise that occurs in these cases. Having the optimal equipment with regard to

implant removal (especially with well fixed implants in the setting of weakened

bone), bone preparation (in the setting of loss of landmarks and weakened

fixation platform), articular constraint, fixation dependability, and bone defect

management is essential. The new Exactech Optetrak Logic CC system may

offer benefits in this regard when compared to older implant systems.

With regard to extraction, Case 1 was used with no specialized extraction de-

vices, and in the hands of the author, medial tibial condylar fracture occurred.

Though this healed with plate fixation, the fracture could have caused a more

complicated treatment course. In the subsequent cases, a specialized pneu-

matic cement–implant disruption system (AcuDriver) and extraction device

(Exactech extractor) were used, which allow for safe disruption of the bone

implant interface, facilitated by the application of axial forces to remove the im-

plant, instead of compressive, bending, or torsional forces, which may predis-

pose bone loss or fracture upon extraction. Since this extraction instrumenta-

tion has been used, and implant removal has been achieved with relative ease,

with very minimal bone loss and no further bone compromise, in all cases.

With regard to bone preparation, the intramedullary and extramedullary fixa-

tion options for cutting guides on both the femoral and tibial sides, provide the

significant stability necessary to achieve accurate bone cuts. The low profile

and anatomic nature of the cutting blocks and associated instrumentation allow

their placement to be facilitated with minimal additional soft tissue dissection.

These factors prove very important in the setting of periprosthetic infection

management, where bone integrity is often compromised, and preservation

of the soft tissue envelope is essential.

With regard to fixation stability and management of bone loss, implant options

are essential in achieving a durable long term construct. For example, in Case

7, to achieve optimal femoral stability from both the stem and the distal femoral

interface, the 4 mm stem offset function was used, allowing for optimal stem

fixation, while conforming well to the patient’s natural distal femoral geometry,

which proved to be altered from previous surgery (Figures 7C, 7D). Tibial cones

prove to be important adjuvants to make up for the central tibial defects that

inevitably occur in revision surgery, allowing for the achievement of stability,

even with the use of shorter stems (Figures, 6D, 6E, 7C, 7D). Extensive distal

femoral augmentation options allow for management of concomitant distal

femoral and posterior femoral bone loss, achieving secure geometric stability,

even in severe cases (Figures 2E, 2F, 4C, 4D).

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FEATURED ARTICLE

With regard to managing constraint, the standard condylar constrained (CC)

allows for articular stability to +/- 1.5° of varus/ valgus constraint, and +/- 2° of

rotational constraint, as is standard with most revision knee systems, and is

very appropriate in the setting of collateral ligament incompetence. A differen-

tiating feature of the Optetrak Logic CC system is the ability to use a PSC tibial

insert, which provides +/- 3° of varus/ valgus and +/- 4° of rotational constraint.

The system even allows for use of the standard posterior stabilized insert,

which provides the least amount of constraint possible in the revision setting.

A convenient intra-operative insert trialing system allows for easy determina-

tion if the less constrained options are appropriate. In Case 3 and Case 5,

because of excellent soft tissue stability and competent collateral ligaments,

the less constrained (PSC) insert was chosen. This option to reduce constraint

in the event of collateral ligament competence could be very important with

regard to optimizing implant longevity, and decreasing unnecessary stresses

on the bone – implant interface.4

CONCLUSION

The challenges associated with treatment of chronic periprosthetic infection

with regard to bone loss and soft tissue compromise offer an ideal model to

test the performance and ability of a revision total knee replacement system,

which can then be readily applied to less complicated cases. From the ex-

traction instrumentation, to the bone preparation instrumentation, to augmen-

tation and fixation options, to varying levels of constraint, the new Optetrak

Logic CC system maintains the ideal of simplicity and ease of use, while still

providing extensive features and options that allow for the management of

virtually any revision knee arthroplasty scenario. •

See additional case reports with Optetrak Logic CC on page 36.

REFERENCES

1. Pulido L, Ghanem E, Joshi A, Purtill JJ, Parvizi J. Peri-prosthetic Joint Infection: The Incidence, Timing, and Predis-posing Factors. Clinical Orthopaedics and Related Research. 2008;466(7):1710-1715.

2. Gehrke T, Alijanipour P, Parvizi J. The management of an infect-ed total knee arthroplasty. Bone Joint J. 2015 Oct;97-B(10 Suppl A):20-9.

3. Workgroup Convened by the Musculoskeletal Infection Society. New definition for periprosthetic joint infection. J Arthroplasty. 2011 Dec;26(8):1136-8.

4. Hannah M, Battista V, Seth S. Constraint in primary total knee arthroplasty. J Am Acad Orthop Surg 2005;13(8):515– 24. 2.

■ APPENDIX■ APPENDIX■ NOTES

EXACTECH, INC.

2320 NW 66TH COURTGAINESVILLE, FL 32653 USA

+1 352.377.1140+1 800.EXACTECH+1 352.378.2617 (FAX)www.exac.com

Exactech, Inc. is proud to have offices and distributors around the globe. For more information about Exactech products available in your country, please visit www.exac.com

For additional device information, refer to the Exactech Knee System–Instructions for Use for a device description, indications, contraindications, precautions and warnings. For further product information, please contact Customer Service, Exactech, Inc., 2320 NW 66th Court, Gainesville, Florida 32653-1630, USA. (352) 377-1140, (800) 392-2832 or FAX (352) 378-2617.

Exactech, as the manufacturer of this device, does not practice medicine, and is not responsible for recommending the appropriate surgical technique for use on a particular patient. These guidelines are intended to be solely informational and each surgeon must evaluate the appropriateness of these guidelines based on his or her personal medical training and experience. Prior to use of this system, the surgeon should refer to the product package insert for comprehensive warnings, precautions, indications for use, contraindications and adverse effects.

The products discussed herein may be available under different trademarks in different countries. All copyrights, and pending and registered trademarks, are property of Exactech, Inc. This material is intended for the sole use and benefit of the Exactech sales force and physicians. It should not be redistributed, duplicated or disclosed without the express written consent of Exactech, Inc. ©2017 Exactech, Inc. 712-25-04 0117

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